Fluoride and arsenic exposure impairs learning and memory and decreases mGluR5 expression in the hippocampus and cortex in rats

Curcumin alleviates arsenic trioxide-induced neural damage in the murine striatal region

RATIONALE

Arsenic-induced neurotoxicity, with dose-dependent effects, is well-documented in rodents. Curcumin (CUR), a cost-effective plant polyphenol, shows neuroprotective effects by modulating oxidative stress, apoptosis, and neurochemistry. This study evaluates curcumin's neuroprotective potential against arsenic trioxide (As2O3) in the mouse striatal region.

METHODS

Healthy adult male mice were chronically administered with varying concentrations of As2O3 (2, 4 and 8 mg/kg bw) alone and along with CUR (100 mg/kg bw) orally for 45 days. Towards the end of the experimental period, the animals were subjected to behavioural paradigms including open field task, novel object recognition, rota-rod, and Morris water maze. Striatal tissues were freshly collected from the animals on day 46 for biochemical analyses (MDA, GPx, and GSH). Additionally, perfusion-fixed brains were processed for morphological observations.

RESULTS

Behavioural study showed an apparent decrease in certain cognitive functions (learning and memory) and locomotor activity in mice exposed to As2O3 compared to controls. Simultaneous treatment of As2O3 (2, 4 and 8 mg/kg bw) and curcumin (100 mg/kg bw) alleviated the As-induced locomotor and cognitive deficits. As2O3 alone exposure also exhibited a significant increase in oxidative stress marker (MDA) and a decrease in antioxidant enzyme levels (GPx, GSH). Morphological alterations were noted in mice subjected to elevated doses of As2O3 (4 and 8 mg/kg bw). However, these changes were reversed in mice who received As2O3 + CUR co-treatment.

CONCLUSIONS

Collectively, our findings indicate that curcumin offers neuroprotection to the striatal region against As2O3-induced behavioral deficits, as well as biochemical and morphological alterations.

Endocrine disrupting effects on morphological synaptic plasticity

Neural regulation of the homeostasis depends on healthy synaptic function. Adaptation of synaptic functions to physiological needs manifests in various forms of synaptic plasticity (SP), regulated by the normal hormonal regulatory circuits. During the past several decades, the hormonal regulation of animal and human organisms have become targets of thousands of chemicals that have the potential to act as agonists or antagonists of the endogenous hormones. As the action mechanism of these endocrine disrupting chemicals (EDCs) came into the focus of research, a growing number of studies suggest that one of the regulatory avenues of hormones, the morphological form of SP, may well be a neural mechanism affected by EDCs. The present review discusses known and potential effects of some of the best known EDCs on morphological synaptic plasticity (MSP). We highlight molecular mechanisms altered by EDCs and indicate the growing need for more research in this area of neuroendocrinology.

NTP monograph on the state of the science concerning fluoride exposure and neurodevelopment and cognition: a systematic review

BACKGROUND

Fluoride is a common exposure in our environment that comes from a variety of sources and is widely promoted for its dental and overall oral health benefits. Contributions to an individual's total exposure come primarily from fluoride in drinking water, food, beverages and dental products. A 2006 evaluation by the National Research Council (NRC) found support for an association between consumption of high levels of naturally occurring fluoride in drinking water and adverse neurological effects in humans and recommended further investigation. The evidence reviewed at that time was from dental and skeletal fluorosis-endemic regions of China. Since the NRC evaluation, the number and location of studies examining cognitive and neurobehavioral effects of fluoride in humans have grown considerably, including several recent North American prospective cohort studies evaluating prenatal fluoride exposure. In 2016, the National Toxicology Program (NTP) published a systematic review of the evidence from experimental animal studies on the effects of fluoride on learning and memory. That systematic review found a low-to-moderate level of evidence that deficits in learning and memory occur in non-human mammals exposed to fluoride.

OBJECTIVE

To conduct a systematic review of the human, experimental animal, and mechanistic literature to evaluate the extent and quality of the evidence linking fluoride exposure to neurodevelopmental and cognitive effects in humans.

METHOD

A systematic review protocol was developed and utilized following the standardized OHAT systematic review approach for conducting literature-based health assessments. This monograph presents the current state of evidence associating fluoride exposure with cognitive or neurodevelopmental health effects and incorporated predefined assessments of study quality and confidence levels. Benefits of fluoride with respect to oral health are not addressed in this monograph.

RESULTS

The bodies of experimental animal studies and human mechanistic evidence do not provide clarity on the association between fluoride exposure and cognitive or neurodevelopmental human health effects. Human mechanistic studies were too heterogenous and limited in number to make any determination on biological plausibility. This systematic review identified studies that assessed the association between estimated fluoride exposure and cognitive or neurodevelopmental effects in both adults and children, which were evaluated separately. The most common exposure assessment measures were drinking water concentrations and estimates of total fluoride exposure, as reflected in biomarkers such as urinary fluoride. In adults, only two high-quality cross-sectional studies examining cognitive effects were available. The literature in children was more extensive and was separated into studies assessing intelligence quotient (IQ) and studies assessing other cognitive or neurodevelopmental outcomes. Eight of nine high-quality studies examining other cognitive or neurodevelopmental outcomes reported associations with estimated fluoride exposure. Seventy-two studies assessed the association between fluoride exposure and IQ in children. Nineteen of those studies were considered to be high quality; of these, 18 reported an inverse association between estimated fluoride exposure and IQ in children. The 18 studies, which include 3 prospective cohort studies and 15 cross-sectional studies, were conducted in 5 different countries. Forty-six of the 53 low-quality studies in children also found evidence of an inverse association between estimated fluoride exposure and IQ in children.

DISCUSSION

Existing animal studies provide little insight into the question of whether fluoride exposure affects IQ. In addition, studies that evaluated fluoride exposure and mechanistic data in humans were too heterogenous and limited in number to make any determination on biological plausibility. The body of evidence from studies in adults is also limited and provides low confidence that fluoride exposure is associated with adverse effects on adult cognition. There is, however, a large body of evidence on associations between fluoride exposure and IQ in children. There is also some evidence that fluoride exposure is associated with other neurodevelopmental and cognitive effects in children; although, because of the heterogeneity of the outcomes, there is low confidence in the literature for these other effects. This review finds, with moderate confidence, that higher estimated fluoride exposures (e.g., as in approximations of exposure such as drinking water fluoride concentrations that exceed the World Health Organization Guidelines for Drinking-water Quality of 1.5 mg/L of fluoride) are consistently associated with lower IQ in children. More studies are needed to fully understand the potential for lower fluoride exposure to affect children's IQ.

Transgenerational Effects of Arsenic Exposure on Learning and Memory in Rats: Crosstalk between Arsenic Methylation, Hippocampal Metabolism, and Histone Modifications

Arsenic (As) is widely present in the natural environment, and exposure to it can lead to learning and memory impairment. However, the underlying epigenetic mechanisms are still largely unclear. This study aimed to reveal the role of histone modifications in environmental levels of arsenic (sodium arsenite) exposure-induced learning and memory dysfunction in male rats, and the inter/transgenerational effects of paternal arsenic exposure were also investigated. It was found that arsenic exposure impaired the learning and memory ability of F0 rats and down-regulated the expression of cognition-related genes Bdnf, c-Fos, mGlur1, Nmdar1, and Gria2 in the hippocampus. We also observed that inorganic arsenite was methylated to DMA and histone modification-related metabolites were altered, contributing to the dysregulation of H3K4me1/2/3, H3K9me1/2/3, and H3K4ac in rat hippocampus after exposure. Therefore, it is suggested that arsenic methylation and hippocampal metabolism changes attenuated H3K4me1/2/3 and H3K4ac while enhancing H3K9me1/2/3, which repressed the key gene expressions, leading to cognitive impairment in rats exposed to arsenic. In addition, paternal arsenic exposure induced transgenerational effects of learning and memory disorder in F2 male rats through the regulation of H3K4me2 and H3K9me1/2/3, which inhibited c-Fos, mGlur1, and Nmdar1 expression. These results provide novel insights into the molecular mechanism of arsenic-induced neurotoxicity and highlight the risk of neurological deficits in offspring with paternal exposure to arsenic.

Association between fluoride exposure in drinking water and cognitive deficits in children: A pilot study

Fluoride (F) exposure in drinking water may lead to reduced cognitive function among children; however, findings largely remain inconclusive. In this pilot study, we examined associations between a range of chronic F exposures (low to high: 0.4 to 15.5 mg/L) in drinking water and cognition in school-aged children (5-14 years, n = 74) in rural Ethiopia. Fluoride exposure was determined from samples of community-based drinking water wells and urine. Cognitive performance was measured using: 1) assessments of ability to draw familiar objects (donkey, house, and person), and 2) a validated Cambridge Neuropsychological Test Automated Battery's (CANTAB) Paired Associate Learning (PAL), which examines memory and new learning and is closely associated with hippocampus function of the brain. Associations between F and cognitive outcomes were evaluated using regression analysis, adjusting for demographic, health status, and other covariates. The median (range) of water and urine F levels was 7.6 (0.4-15.5 mg/L) and 6.3 (0.5-15.7 mg/L), respectively; these measures were strongly correlated (r = 0.74), indicating that water is the primary source of F exposure. Fluoride in drinking water was negatively associated with cognitive function, measured by both drawing and CANTAB test performance. Inverse relationships were also found between F and drawing objects task scores, after adjusting for covariates (p < 0.05). Further analysis using CANTAB PAL tasks in the children confirmed that F level in drinking water was positively associated with the number of errors made by children (p < 0.01), also after adjusting for covariates (p < 0.05). This association between water F and total errors made became markedly stronger as PAL task difficulty increased. Fluoride exposure was also inversely associated with other PAL tasksthe number of patterns reached, first attempt memory score and mean errors to success. These findings provide supportive evidence that high F exposures may be associated with cognitive deficits in children. Additional well-designed studies are critically needed to establish the neurotoxicity of F in children and adults exposed to both low levels known to protect dental caries, as well as excess F levels in drinking water.

Fisetin attenuates arsenic and fluoride subacute co-exposure induced neurotoxicity via regulating TNF-α mediated activation of NLRP3 inflammasome

Groundwater is considered safe, however, the occurrence of contaminants like arsenic and fluoride has raised a major healthcare concern. Clinical studies suggested that arsenic and fluoride co-exposure induced neurotoxicity, however efforts to explore safe and effective management of such neurotoxicity are limited. Therefore, we investigated the ameliorative effect of Fisetin against arsenic and fluoride subacute co-exposure-induced neurotoxicity, and associated biochemical and molecular changes. Male BALB/c mice Arsenic (NaAsO₂: 50mg/L) and fluoride (NaF: 50mg/L) were exposed to drinking water and fisetin (5, 10, and 20mg/kg/day) was administered orally for 28 days. The neurobehavioral changes were recorded in the open field, rotarod, grip strength, tail suspension, forced swim, and novel object recognition test. The co-exposure resulted in anxiety-like behaviour, loss of motor coordination, depression-like behaviour, and loss of novelty-based memory, along with enhanced prooxidant, inflammatory markers and loss of cortical and hippocampal neurons. The treatment with fisetin reversed the co-exposure-induced neurobehavioral deficit along with restoration of redox & inflammatory milieu, and cortical and hippocampal neuronal density. Apart from antioxidants, inhibition of TNF-α/ NLRP3 expression has been suggested as one of the plausible neuroprotective mechanisms of Fisetin in this study.

Prolonged fluoride exposure induces spatial-memory deficit and hippocampal dysfunction by inhibiting small heat shock protein 22 in mice

Millions of residents in areas with high-fluoride drinking water supply ingest excessive levels of fluoride for long periods. This study investigated the mechanisms and impacts of lifelong exposure to naturally occurring moderate-high-fluoride drinking water on spatial-memory function by studying mice in controlled experiments. Spatial-memory deficits and disorders of hippocampal neuronal electrical activity were observed in mice exposed to 25-ppm or 50-ppm-fluoride drinking water for 56 weeks, but not in adult or old mice exposed to 50 ppm fluoride for 12 weeks. Ultrastructural analysis showed severely damaged hippocampal mitochondria, evidenced by reduced mitochondrial membrane potential and ATP content. Mitochondrial biogenesis was impaired in fluoride-exposed mice, manifesting as a significantly reduced mtDNA content, mtDNA-encoded subunits mtND6 and mtCO1, and respiratory complex activities. Fluoride reduced expression of Hsp22, a beneficial mediator of mitochondrial homeostasis, and decreased levels of signaling for the PGC-1α/TFAM pathway-which regulates mitochondrial biogenesis-and the NF-κβ/STAT3 pathway-which regulates mitochondrial respiratory chain enzyme activity. Hippocampus-specific Hsp22-overexpression improved fluoride-induced spatial-memory deficits by activating the PGC-1α/TFAM and STAT3 signaling pathways, while Hsp22-silencing aggravated the deficits by inhibiting both pathways. Downregulation of Hsp22 plays a vital role in fluoride-induced spatial-memory deficits by impacting mtDNA-encoding subsets and mitochondrial respiratory chain enzyme activity.

Molar tooth shortening induces learning and memory impairment in Wistar rat

OBJECTIVE

This study aimed to investigate the relationship between different patterns of molar crown loss and the association between symmetrical and asymmetrical shortening molar teeth with memory impairment.

MATERIALS AND METHODS

Male Wistar rats were divided into four groups (n = 10) including control, SLM (shortened left molar), SRM (shortened right molar), and SBM (shortened bilateral molar) groups. Morris water maze (MWM) and passive avoidance test (PAT) were performed to assess spatial and fear memory, respectively. Besides, histological assessment of hippocampus and gingival tissues was done.

RESULTS

In the MWM test, SBM and SLM groups had higher escape latency over training trials and spent less time in the target quadrant in the probe trial (p < 0.01). In the PAT, step-through latency was significantly reduced in three groups, and time spent in the dark compartment increased in SBM (p < 0.01) and SLM (p < 0.05) groups. In addition, each teeth shortening group indicated a reduction in density (p < 0.01) and thickness layer (p < 0.05) of pyramidal cells. Gingival was normal after shortening of the molar crown.

CONCLUSIONS

Different patterns of molar teeth shortening induced learning and memory impairment; however, symmetrical molar teeth shortening has more effects on memory impairment.

Fluoride Induced Neurobehavioral Impairments in Experimental Animals: a Brief Review

Fluoride is one of the major toxicants in the environment and is often found in drinking water at higher concentrations. Living organisms including humans exposed to high fluoride levels are found to develop mild-to-severe detrimental pathological conditions called fluorosis. Fluoride can cross the hematoencephalic barrier and settle in various brain regions. This accumulation affects the structure and function of both the central and peripheral nervous systems. The neural ultrastructure damages are reflected in metabolic and cognitive activities. Hindrances in synaptic plasticity and signal transmission, early neuronal apoptosis, functional alterations of the intercellular signaling pathway components, improper protein synthesis, dyshomeostasis of the transcriptional and neurotrophic factors, oxidative stress, and inflammatory responses are accounted for the fluoride neurotoxicity. Fluoride causes a decline in brain functions that directly influence the overall quality of life in both humans and animals. Animal studies are widely used to explore the etiology of fluoride-induced neurotoxicity. A good number of these studies support a positive correlation between fluoride intake and toxicity phenotypes closely associated with neurotoxicity. However, the experimental dosages highly surpass the normal environmental concentrations and are difficult to compare with human exposures. The treatment procedures are highly dependent on the dosage, duration of exposure, sex, and age of specimens among other factors which make it difficult to arrive at general conclusions. Our review aims to explore fluoride-induced neuronal damage along with associated histopathological, behavioral, and cognitive effects in experimental models. Furthermore, the correlation of various molecular mechanisms upon fluoride intoxication and associated neurobehavioral deficits has been discussed. Since there is no well-established mechanism to prevent fluorosis, phytochemical-based alleviation of its characteristic indications has been proposed as a possible remedial measure.

Effects of chronic fluorosis on the brain

This article reviews the effects of chronic fluorosis on the brain and possible mechanisms. We used PubMed, Medline and Cochraine databases to collect data on fluorosis, brain injury, and pathogenesis. A large number of in vivo and in vitro studies and epidemiological investigations have found that chronic fluorosis can cause brain damage, resulting in abnormal brain structure and brain function.Chronic fluorosis not only causes a decline in concentration, learning, and memory, but also has mental symptoms such as anxiety, tension, and depression. Several possible mechanisms that have been proposed: the oxidative stress and inflammation theory, neural cell apoptosis theory, neurotransmitter imbalance theory, as well as the doctrine of the interaction of fluorine with other elements. However, the specific mechanism of chronic fluorosis on brain damage is still unclear. Thus, a better understanding of the mechanisms via which chronic fluorosis causes brain damage is of great significance to protect the physical and mental health of people in developing countries, especially those living in the endemic areas of fluorosis. In brief, further investigation concerning the influence of fluoride on the brain should be conducted as the neural damage induced by it may bring about a huge problem in public health, especially considering growing environmental pollution.

Domain-specific effects of prenatal fluoride exposure on child IQ at 4, 5, and 6-12 years in the ELEMENT cohort

OBJECTIVE

Prenatal exposure to fluoride has been associated with adverse neurodevelopmental outcomes. However, the neuropsychological profile of fluoride's developmental neurotoxicity at low levels and the stability of this relationship across childhood has not been characterized. We investigated the longitudinal and domain specific effect of prenatal fluoride exposure on IQ among children ages 4, 5, and 6-12 years in the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) cohort.

METHODS

We measured the average of maternal urinary fluoride at each trimester of pregnancy adjusted for creatinine (MUF_CRE). Children were administered the McCarthy Scales of Children's Abilities at ages 4 (N = 386) and 5 (N = 308), and the Wechsler Abbreviated Scale of Intelligence at age 6-12 (N = 278). We used generalized estimating equation (GEE) models to estimate the population averaged effect of MUF_CRE concentration on longitudinal General Cognitive Index (GCI)/Full-Scale IQ (FSIQ), Verbal IQ (VIQ), and Performance IQ (PIQ) scores (N = 348). We tested for possible interactions between MUF_CRE and child sex as well as for MUF_CRE and time point on children's IQ. All models controlled for relevant available covariates.

RESULTS

The mean/median MUF_CRE concentration was 0.90/0.83 mg/L (SD = 0.39; IQR, 0.64-1.11 mg/L). A 0.5 mg/L increase in MUF_CRE predicted an average 2.12-point decrease in GCI/FSIQ (95% CI: -3.49, -0.75) and 2.63-point decrease in PIQ (95% CI: -3.87, -1.40). MUF_CRE was marginally associated with VIQ across time (B = -1.29, 95% CI: -2.60, 0.01). No interactions between MUF_CRE and child sex or MUF_CRE and time were observed.

CONCLUSION

The negative association between prenatal fluoride exposure and longitudinal IQ was driven by decrements in non-verbal intelligence (i.e. PIQ), suggesting that visual-spatial and perceptual reasoning abilities may be more impacted by prenatal fluoride exposure as compared to verbal abilities.

Toxicity studies of select ionic liquids (1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-butyl-1-methylpyrrolidinium chloride, and n-butylpyridinium chloride) administered in drinking water to Sprague Dawley (Hsd:Sprague Dawley SD) rats and B6C3F1/N mice

Ionic liquids (ILs) are synthetic solvents with applications in a variety of industrial and chemical industries. Human exposure to this diverse chemical class is primarily through dermal or oral routes. Research suggests toxicity may be associated with IL structural characteristics, including the type of cation base or alkyl chain substitutions associated with the cation. To further investigate this hypothesis, the National Toxicology Program (NTP) conducted 3-month toxicity studies in male and female Sprague Dawley (Hsd:Sprague Dawley SD) rats and B6C3F1/N mice (n = 10/sex/exposure group; 3 exposure concentrations per IL) to compare the relative toxicities of four ILs administered via drinking water-1-ethyl-3-methylimidazolium chloride (Emim-Cl), 1-butyl-3-methylimidazolium chloride (Bmim-Cl), 1-butyl-1-methylpyrrolidinium chloride (Bmpy-Cl), and n-butylpyridinium chloride (NBuPy-Cl). (Abstract Abridged).

Genome-wide Alteration of Histone Methylation Profiles Associated with Cognitive Changes in Response to Developmental Arsenic Exposure in Mice

Inorganic arsenic is a xenobiotic entering the body primarily through contaminated drinking water and food. There are defined mechanisms that describe arsenic’s association with increased cancer incidence, however mechanisms explaining arsenic exposure and neurodevelopmental or aging disorders are poorly defined. In recent years, arsenic effects on epigenome have become a particular focus. We hypothesize that human relevant arsenic exposure during particular developmental windows, or long-term exposure later in life induce pathophysiological neural changes through epigenomic alterations, in particular histone methylation profile, manifesting as cognitive decline. C57BL/6 wild-type mice were continually exposed to sodium arsenite (100 µg/L) in drinking water prior to mating through weaning of the experimental progeny. A second cohort of aged APP/PS mice were chronically exposed to the same level of arsenic. Cognitive testing, histological examination of brains and genome-wide methylation levels of H3K4me3 and H3K27me3 examined after ChIP-seq were used to determine the effects of arsenic exposure. Developmental arsenic exposure caused significantly diminished cognition in wild-type mice. The analysis of ChIP-seq data and experiments with mouse embryonic stem cells demonstrated that epigenetic changes induced by arsenic exposure translated into gene expression alterations associated with neuronal development and neurological disease. Increased hippocampal amyloid plaques levels of APP/PS mice and cognitive decline provided evidence that arsenic exposure aggravated an existing Alzheimer’s disease-like phenotype. We show developmental arsenic exposure significantly impacts histone modifications in brain which remain present into adulthood and provide a potential mechanism by which developmental arsenic exposure influences cognitive functions. We also show that human relevant, chronic arsenic exposure has deleterious effects on adult APP/PS mice and exacerbates existing Alzheimer’s disease-like symptoms. The results demonstrate how developmental arsenic exposure impacts the brain epigenome, leading to altered gene expression later in life.

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Developmental arsenic exposure impacts biologically significant histone modifications in brain.

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Decreased trimethylation of H3K27 is associated with processes related to neuron fate and development.

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Histone modification in brain present a potential mechanism how developmental arsenic exposure impacts cognitive functions.

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Arsenic exacerbates cognitive deficits and neuroinflammation in AD model mice.

The association between blood lymphocyte NMDAR, group I mGluRs and cognitive function changes in occupationally aluminum-exposed workers and verification in rats

BACKGROUND

Many studies have shown that occupational aluminum (Al) exposure could affect the cognitive functions of workers and cause mild cognitive impairment (MCI). Glutamate receptors (GluRs) play an important role in learning and memory functions.

METHODS

352 workers in a large Al production enterprise were investigated in this research. MMSE, CDT, DST, VFT, FOM were used to evaluate the cognitive functions of workers. Plasma Al levels as exposure indices were measured by Graphite Furnace Atomic Absorption Method (GFAAS). The expression of GluRs was measured by ELISA. Cognitive function comprehensive scores were obtained through factor analysis. Then a rat model of chronic AlCl₃ exposure was established. The detection method of Al levels and protein expression were the same as mentioned-above.

RESULTS

Compared with the Q1 group, the DST, VFT, and comprehensive cognitive function scores of the Q4 group were lower(P < 0.05). For every 1μg/L increase in plasma Al concentration, the risk of cognitive impairment increases 1.051 times (95 %CI:1.031,1.072). Both NMDAR1 and NMDAR2A protein expression level of Q1 group were higher than those of Q2, Q3, Q4 group (all P < 0.05). The mediating effect ratio of NMDAR1 between plasma Al levels and cognitive function comprehensive scores was a1*b1/c=11.30 %, and the mediating effect ratio of NMDAR2A was |a2*b2/c|=21.77 %. Compared with control group, the escape latency of rats in the high Al dose group was longer day by day (P < 0.05). With the increase of Al dose, the relative expression of NMDAR1, NMDAR2A, NMDAR2B, GluR1 and mGluR5 in cerebral cortex and lymphocytes of rats were decreased (P < 0.05). The result of correlation analysis on NMDAR1 protein expression between brain cortex and lymphocyte showed that the correlation coefficient is r = 0.646(P < 0.05).

CONCLUSION

Taking together the results from both Al exposed workers and animal, there is a certain correlation between NMDAR1 protein contents of brain cortex and peripheral lymphocytes. We propose that lymphocyte NMDAR1 could be considered as a peripheral potential marker of cognitive impairment for further observation.

Effect of Selenium on Brain Injury in Chickens with Subacute Arsenic Poisoning

The aim of this study was to investigate the effects of different doses of selenium (Se) on oxidative damage and neurotransmitter-related parameters in arsenic (As)-induced broiler brain tissue damage. Two hundred 1-day-old avian broilers were randomly divided into five groups and fed the following diets: control group (As 0.1 mg/kg + Se 0.2 mg/kg), As group (As 3 mg/kg + Se 0.2 mg/kg), low-Se group (As 3 mg/kg + Se 5 mg/kg), medium-Se group (As 3 mg/kg + Se 10 mg/kg), and high-Se group (As 3 mg/kg + Se 15 mg/kg). Glutathione (GSH), glutathione peroxidase (GSH-PX), nitric oxide (NO), nitric oxide synthase (NOS) activity, glutamate (Glu) concentration, glutamine synthetase (GS) activity, acetylcholinesterase (TchE) activity, and the apoptosis rate of brain cells were measured. The results showed that 3 mg/kg dietary As could induce oxidative damage and neurotransmitter disorder of brain tissue, increase the apoptosis rate of brain cells and cause damage to brain tissue, decrease activities of GSH and GSH-PX, decrease the contents of NO, decrease the activities of iNOS and tNOS, increase contents of Glu, and decrease activities of Gs and TchE. Compared with the As group, the Se addition of the low-Se and medium-Se groups protected against As-induced oxidative damage, neurotransmitter disorders, and the apoptosis rate of brain cells, with the addition of 10 mg/kg Se having the best effect. However, 15 mg/kg Se not only did not produce a protective effect against As damage but actually caused similar or severe damage.

Caregivers' feeding behaviour, children's eating behaviour and weight status among children of preschool age in China

BACKGROUND

Childhood overweight and obesity have become significant public health challenges worldwide. The present study aimed to investigate whether caregivers' feeding behaviour and children's eating behaviour were associated with the weight status of preschool children in China.

METHODS

A cross-sectional questionnaire was administered to 912 caregivers of preschool children from April to July 2016. Caregivers' feeding behaviours were assessed by the Chinese Preschooler's Caregiver Feeding Behaviour Scale. Children's eating behaviours were evaluated using the Chinese Preschooler's Eating Behaviour Questionnaire. After controlling for demographic characteristics, multiple linear regression and logistic regression analyses were performed to evaluate the relationship between caregivers' feeding behaviour, children's eating behaviour and children's body mass index (BMI).

RESULTS

The results showed that weight concerns on the part of caregivers (β = 0.53) and food responsiveness on the part of children (β = 0.93) were positively correlated with children's BMI, whereas caregivers' responsibility for feeding (β = -0.68) and children's external eating (β = -0.53) were negatively correlated with BMI. Among caregiver feeding behaviours, weight concerns [odds ratio (OR) =4.54, p < 0.001] and behaviour-restricted feeding (OR =0.29, p < 0.001) were positively correlated with children's BMI. A child's food responsiveness (OR =4.04, p < 0.001) was also positively correlated with his/her BMI, whereas the child's satiety responsiveness (OR =0.42, p < 0.001) and emotional eating habits (OR =0.56, p < 0.001) were negatively correlated with overweight/obesity status.

CONCLUSIONS

Our study demonstrated that children's eating behaviour and caregivers' feeding behaviour were associated with weight status among preschool children in China. Behaviour interventions on caregivers and their children may prevent or reduce weight problems in preschool children.

Resveratrol Attenuates Learning, Memory, and Social Interaction Impairments in Rats Exposed to Arsenic

Arsenic (As) toxicity has deleterious effects on human health causing disorder in the brain. The aim of this study was to investigate the possible neuroprotective effect of resveratrol (RSV) on arsenic-induced neurotoxicity in rats. Neurotoxicity in rats was developed by treating As 10 mg/kg/day for 21 days orally. Animals were put into seven groups: control, vehicle, As, As+RSV10, As+RSV20 mg/kg, RSV10, and RSV20 mg/kg. Behavioral assessments such as the social interaction test, novel object recognition test, elevated plus maze, open field, the Morris water maze, in addition to assessment of biomarkers such as ferric reducing ability of plasma assay, glutathione assay, and malondialdehyde assay, were used to evaluate the effects of RSV on cognitive impairment and molecular changes induced by As. The results showed that cognitive performance impaired in As rats. RSV20 mg/kg significantly could ameliorate behavioral changes like spatial learning in days 3 and 4 (p < 0.05), recognition learning and memory (p < 0.01), disabilities in motor coordination and stress (p < 0.05), increased anxiety (p < 0.05), and social interaction deficit (sociability (p < 0.001) and social memory (p < 0.05)). RSV20 mg/kg also attenuated molecular modifications like decreased antioxidant power (p < 0.001), reduced glutathione content (p < 0.05), and increased malondialdehyde level (p < 0.05) induced by As. In addition to oxidative stress assessments, RSV10 mg/kg could significantly increase FRAP (p < 0.01) and GSH (p < 0.05); however, MDA was not significantly increased. Our current behavioral findings suggest that RSV has neuroprotective effects against AS toxicity.

Molecular Mechanism of Arsenic-Induced Neurotoxicity including Neuronal Dysfunctions

Arsenic is a key environmental toxicant having significant impacts on human health. Millions of people in developing countries such as Bangladesh, Mexico, Taiwan, and India are affected by arsenic contamination through groundwater. Environmental contamination of arsenic leads to leads to various types of cancers, coronary and neurological ailments in human. There are several sources of arsenic exposure such as drinking water, diet, wood preservatives, smoking, air and cosmetics, while, drinking water is the most explored route. Inorganic arsenic exhibits higher levels of toxicity compared its organic forms. Exposure to inorganic arsenic is known to cause major neurological effects such as cytotoxicity, chromosomal aberration, damage to cellular DNA and genotoxicity. On the other hand, long-term exposure to arsenic may cause neurobehavioral effects in the juvenile stage, which may have detrimental effects in the later stages of life. Thus, it is important to understand the toxicology and underlying molecular mechanism of arsenic which will help to mitigate its detrimental effects. The present review focuses on the epidemiology, and the toxic mechanisms responsible for arsenic induced neurobehavioral diseases, including strategies for its management from water, community and household premises. The review also provides a critical analysis of epigenetic and transgenerational modifications, mitochondrial oxidative stress, molecular mechanisms of arsenic-induced oxidative stress, and neuronal dysfunction.

Fate of arsenic in living systems: Implications for sustainable and safe food chains

Arsenic, a group 1 carcinogen for humans, is abundant as compared to other trace elements in the environment and is present mainly in the Earth's crust and soil. The arsenic distributions in different geographical regions are dependent on their geological histories. Anthropogenic activities also contribute significantly to arsenic release into the environment. Arsenic presents several complications to humans, animals, and plants. The physiology of plants and their growth and development are affected by arsenic. Arsenic is known to cause cancer and several types of organ toxicity, such as cardiotoxicity, nephrotoxicity, and hepatotoxicity. In the environment, arsenic exists in variable forms both as inorganic and organic species. From arsenic containing compartments, plants can absorb and accumulate arsenic. Crops grown on these contaminated soils pose several-fold higher toxicity to humans compared with drinking water if arsenic enters the food chain. Information regarding arsenic transfer at different trophic levels in food chains has not been summarized until now. The present review focuses on the food chain perspective of arsenic, which affects all components of the food chain during its course. The circumstances that facilitate arsenic accumulation in flora and fauna, as components of the food chain, are outlined in this review.

Critical windows of fluoride neurotoxicity in Canadian children

BACKGROUND

Fluoride has been associated with IQ deficits during early brain development, but the period in which children are most sensitive is unknown.

OBJECTIVE

We assessed effects of fluoride on IQ scores across prenatal and postnatal exposure windows.

METHODS

We used repeated exposures from 596 mother-child pairs in the Maternal-Infant Research on Environmental Chemicals pregnancy and birth cohort. Fluoride was measured in urine (mg/L) collected from women during pregnancy and in their children between 1.9 and 4.4 years; urinary fluoride was adjusted for specific gravity. We estimated infant fluoride exposure (mg/day) using water fluoride concentration and duration of formula-feeding over the first year of life. Intelligence was assessed at 3-4 years using the Wechsler Preschool and Primary Scale of Intelligence-III. We used generalized estimating equations to examine the associations between fluoride exposures and IQ, adjusting for covariates. We report results based on standardized exposures given their varying units of measurement.

RESULTS

The association between fluoride and performance IQ (PIQ) significantly differed across prenatal, infancy, and childhood exposure windows collapsing across child sex (p = .001). The strongest association between fluoride and PIQ was during the prenatal window, B = -2.36, 95% CI: -3.63, -1.08; the association was also significant during infancy, B = -2.11, 95% CI: -3.45, -0.76, but weaker in childhood, B = -1.51, 95% CI: -2.90, -0.12. Within sex, the association between fluoride and PIQ significantly differed across the three exposure windows (boys: p = .01; girls: p = .01); among boys, the strongest association was during the prenatal window, B = -3.01, 95% CI: -4.60, -1.42, whereas among girls, the strongest association was during infancy, B = -2.71, 95% CI: -4.59, -0.83. Full-scale IQ estimates were weaker than PIQ estimates for every window. Fluoride was not significantly associated with Verbal IQ across any exposure window.

CONCLUSION

Associations between fluoride exposure and PIQ differed based on timing of exposure. The prenatal window may be critical for boys, whereas infancy may be a critical window for girls.

Virgin Coconut Oil Resists Arsenic-Induced Cerebral Neurotoxicity and Cholesterol Imbalance via Suppression of Oxidative Stress, Adenosine Deaminase and Acetylcholinesterase Activities in Rats

Arsenic (As) is a classic neurotoxicant; its pathogenesis is associated with oxidative stress and oxidative stress-mediated cholinergic deficits. This study explored antioxidant activity of virgin coconut oil (VCO) against sodium arsenite-induced oxidative stress-mediated cerebral neurotoxicity in rats. Eighteen rats were divided into 3 groups- Normal control, As control and VCO + As. The VCO (5 mL/kg) was given once daily by oral gavage from day 1 to day 21, while As (10 mg/kg) was given once daily by oral gavage from day 15 to day 21. Cerebral superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), malondialdehyde (MDA), adenosine deaminase (ADA) and acetylcholinesterase (AchE) activities were analysed. Nitric oxide (NO), lipid profile, phospholipid (PL), and reduced glutathione (GSH) were also evaluated in cerebral homogenate. The cerebrum was sectioned for histological analysis. Administration of As induced significant depressions in antioxidant enzymes, GSH, PL, and HDL-c compared to normal control. Levels of MDA, NO, total cholesterol and activities of ADA, AchE in the cerebrum were markedly increased by As compared to normal rats. Lipid profile indices and PL were prominently altered by As. Histopathological study supported the biochemical findings through extensive cerebral damage. In contrast, oral supplementation of VCO prior to and along with As treatment significantly attenuated the As-induced biochemical alterations and restored near-normal histology. VCO attenuates cerebral neurotoxicity by strengthening endogenous antioxidant defence and cholinergic function via counteracting free-radical-mediated arsenic toxicity.

Combined effect of arsenic and fluoride at environmentally relevant concentrations in zebrafish (Danio rerio) brain: Alterations in stress marker and apoptotic gene expression

Arsenic and fluoride are two naturally occurring toxicants to which various organisms including a major part of the human populations are co-exposed to. However, interactions between them inside body are quite complicated and needs proper evaluation. Inconclusive reports regarding their combined effects on brain prompted us to conduct this study where we investigated their individual as well as combined effects on female zebrafish brain at environmentally relevant concentrations (50 μgL^-1 arsenic trioxide and 15 mgL^-1 sodium fluoride) after different time intervals (15, 30 and 60 days). Persistent near-basal level of GSH, least increased MDA content and catalase activity portrayed arsenic and fluoride co-exposure as less toxic which was corroborated with far less damage caused in the histoarchitecture of optic tectum region in midbrain. Stress-responsive genes viz., Nrf2 and Hsp70 were overexpressed after individual as well as combined exposures, indicating a common cellular response to combat the formed oxidative stresses. Biphasic response of AChE upon individual exposure confirmed their neurotoxic effects too. Expression profile of p53 (unaltered), Bax (lower or near-basal) and Bcl2 (comparatively higher), along with absence of DNA fragmentation indicated no induction of apoptosis in the co-exposed group. Tissue accumulation of arsenic and fluoride was significantly less in the brain of co-exposed zebrafish when compared to their individual exposures. This preliminary study indicates an antagonistic effect of these two toxicants in zebrafish brain and needs further studies involving oxidative stress independent markers to understand the detailed molecular mechanism.

Astaxanthin Decreases Spatial Memory and Glutamate Transport Impairment Induced by Fluoride

Excessive exposure to the sources of fluoride in drinking water, oral care products, and food is a widespread problem. Fluoride is associated with impairment in child intelligence development. It causes DNA damage, oxidative stress, and mitochondrial dysfunction, mainly due to the production of reactive oxygen species (ROS). It has been postulated that the use of antioxidants such as astaxanthin, may alleviate fluoride's adverse effects. This study assessed the effects of fluoride on cellular ROS content and rat's learning and memory ability and investigated the protective potency of astaxanthin with emphasis on the role of glutamate using the Morris Water Maze test, glutamate concentration determination, and western blot techniques. The fluoride treatment of cells results in an increment of cellular ROS, whereas astaxanthin inhibits lipid peroxidation. Fluoride significantly decreases the cellular glutamate uptake and glutamate transporter, protein level, possibly due to the disruption of mitochondrial energy metabolism and defect of the transporter recycle, respectively. The in-vivo study indicated that the treatment of rats with fluoride led to a loss of learning, while astaxanthin improved memory dysfunction. Measurement of ROS and glutamate levels of rat brain hippocampus showed that fluoride increased the ROS but decreased the glutamate. On the other hand, the utilization of astaxanthin decreased the brain ROS content and increased the glutamate level. It seems that fluoride disrupts the normal function of neurons via increment of ROS production and decrement of glutamate level, whereas astaxanthin has neuroprotective potency due to the ROS scavenging ability.

Cognitive Decline of Rats with Chronic Fluorosis Is Associated with Alterations in Hippocampal Calpain Signaling

The study was designed to evaluate an influence of excessive fluoride (F^-) intake on cognitive capacities of adult rats and on proteins of memory-related calpain signaling in hippocampus. Control animals were given water with natural F^- content of 0.4 ppm; rats from other groups consumed the same water supplemented with 5, 20, and 50 ppm F^- (as NaF) for 12 months. The efficiency of learning and memory formation was evaluated by novel object recognition (NOR) and Morris water maze tests. The expression of enzymes of calpain-1 and calpain-2 signaling in hippocampus was detected by Western blotting. Excessive F^- consumption had moderate impact on short-term memory, but impaired spatial learning and long-term memory of animals. Intoxication of rats with 5-50 ppm F^- led to stimulation of calpain-1 in hippocampal cells and its translocation from cytosol to membranes, accompanied by activation of GTPase RhoA. Exposure to 20-50 ppm F^- resulted in proteolytic cleavage of phosphatase PHLPP1 and increased expression of phospho-ERK1/2 kinase with insignificant decline of total ERK1/2 activity. In contrast, F^- did not change the expression of calpain-2 and its substrates-phosphatase PTEN and kinase mTOR. However, F^- intake led to downregulation of cAMP-response element binding protein (CREB) and brain-derived neurotrophic factor (BDNF). Thus, altered expression of calpain-1 and its downstream effectors at a background of stable activity of calpain-2 indicates overstimulation of signaling pathways of early LTP phase and disrupted link between early and late LTP phases, most probably due to altered activity of transcriptional and neurotrophic factors.

Curcumin supplementation shows modulatory influence on functional and morphological features of hippocampus in mice subjected to arsenic trioxide exposure

Since, oxidative stress has been suggested as one of the mechanisms underlying arsenic-induced toxicity, the present study focused on the role of antioxidant (curcumin) supplementation on behavioral, biochemical, and morphological alterations with context to mice hippocampus (CA1) following arsenic trioxide (As₂O₃) administration. Healthy male Swiss albino mice were divided into control and experimental groups. As₂O₃ (2 mg/kg bw) alone or along with curcumin (100 mg/kg bw) was administered to experimental groups by oral route for 45 days whereas the control groups received either no treatment or vehicle for curcumin. Animals were subjected to behavioral study towards the end of the experimental period (day 33-45). On day 46, the brain samples were obtained and subjected either to immersion fixation (for morphometric observations) or used afresh for biochemical test. Behavioral tests (open field, elevated plus maze, and Morris water maze) revealed enhanced anxiety levels and impairment of cognitive functions in As₂O₃ alone treated groups whereas a trend of recovery was evident in mice simultaneously treated with As₂O₃ and curcumin. Morphological observations showed noticeable reduction in stratum pyramidale thickness (CA1), along with decrease in density and size of pyramidal neurons in As₂O₃ alone exposed group as compared to As₂O₃+Cu co-treated group. Hippocampal glutathione levels were found to be downregulated in animals receiving As₂O₃ as against the levels of controls and curcumin supplemented animals, thereby, suggestive of beneficial role of curcumin on As₂O₃ induced adverse effects.

Protective effect of Mucuna pruriens against arsenic-induced liver and kidney dysfunction and neurobehavioral alterations in rats

BACKGROUND AND AIM

Intoxication of arsenic in rats is known to result in neurological effects as well as liver and kidney dysfunction. Mucuna pruriens has been identified for its medicinal properties. The aim of the study was to investigate the protective effect of aqueous seed extract of M. pruriens on sodium arsenite-induced memory impairment, liver, and kidney functions in rats.

MATERIALS AND METHODS

The experiment was divided into short-term treatment (45 days) and long-term treatment (90 days), with each group divided into nine sub-groups consisting of six animals each. Sub-groups 1 and 2 served as normal, and N-acetylcysteine (NAC) controls, respectively. Sub-groups 3-9 received sodium arsenite in drinking water (50 mg/L). In addition, sub-group 4 received NAC (210 mg/kg b.wt) orally once daily, sub-groups 5-7 received aqueous seed extract of M. pruriens (350 mg/kg b.wt, 530 mg/kg b.wt, and 700 mg/kg b.wt) orally once daily and sub-groups 8 and 9 received a combination of NAC and aqueous seed extract of M. pruriens (350 mg/kg b.wt and 530 mg/kg b.wt) orally once daily. Following the treatment, the blood was drawn retro-orbitally to assess the liver (serum alanine transaminase [ALT], serum aspartate transaminase, and serum alkaline phosphatase) and kidney (serum urea and serum creatinine) functions. Learning and memory were assessed by passive avoidance test. Animals were sacrificed by an overdose of ketamine, and their Nissl stained hippocampal sections were analyzed for alterations in neural cell numbers in CA1 and CA3 regions.

RESULTS

In the short-term treatment, groups administered with M. pruriens 530 mg/kg b.wt alone and combination of NAC + M. pruriens 350 mg/kg b.wt exhibited a significant improvement in memory retention, less severe neurodegeneration, and decrease in serum ALT levels. In long-term treatment, groups administered with M. pruriens 700 mg/kg b.wt alone and combination of NAC+M. pruriens 350 mg/kg b.wt, respectively, showed better memory retention, decreased neural deficits, and reduced levels of kidney and liver enzymes.

CONCLUSION

The seed extract of M. pruriens showed significant enhancement in memory and learning. The number of surviving neurons in the CA1 and CA3 regions also increased on treatment with M. pruriens. Serum ALT, serum urea, and serum creatinine levels showed significant improvement on long-term treatment with M. pruriens.

A Systematic Review of the Various Effect of Arsenic on Glutathione Synthesis In Vitro and In Vivo

Background

Arsenic is a toxic metalloid widely present in nature, and arsenic poisoning in drinking water is a serious global public problem. Glutathione is an important reducing agent that inhibits arsenic-induced oxidative stress and participates in arsenic methylation metabolism. Therefore, glutathione plays an important role in regulating arsenic toxicity. In recent years, a large number of studies have shown that arsenic can regulate glutathione synthesis in many ways, but there are many contradictions in the research results. At present, the mechanism of the effect of arsenic on glutathione synthesis has not been elucidated.

Objective

We will conduct a meta-analysis to illustrate the effects of arsenic on GSH synthesis precursors Glu, Cys, Gly, and rate-limiting enzyme γ-GCS in mammalian models, as well as the regulation of p38/Nrf2 of γ-GCS subunit GCLC, and further explore the molecular mechanism of arsenic affecting glutathione synthesis.

Results

This meta-analysis included 30 studies in vivo and 58 studies in vitro, among which in vivo studies showed that arsenic exposure could reduce the contents of GSH (SMD = -2.86, 95% CI (-4.45, -1.27)), Glu (SMD = -1.11, 95% CI (-2.20,-0.02)), and Cys (SMD = -1.48, 95% CI (-2.63, -0.33)), with no statistically significant difference in p38/Nrf2, GCLC, and GCLM. In vitro studies showed that arsenic exposure increased intracellular GSH content (SMD = 1.87, 95% CI (0.18, 3.56)) and promoted the expression of p-p38 (SMD = 4.19, 95% CI (2.34, 6.05)), Nrf2 (SMD = 4.60, 95% CI (2.34, 6.86)), and GCLC (SMD = 1.32, 95% CI (0.23, 2.41)); the p38 inhibitor inhibited the expression of Nrf2 (SMD = -1.27, 95% CI (-2.46, -0.09)) and GCLC (SMD = -5.37, 95% CI (-5.37, -2.20)); siNrf2 inhibited the expression of GCLC, and BSO inhibited the synthesis of GSH. There is a dose-dependent relationship between the effects of exposure on GSH in vitro. Conclusions. These indicate the difference between in vivo and in vitro studies of the effect of arsenic on glutathione synthesis. In vivo studies have shown that arsenic exposure can reduce glutamate and cysteine levels and inhibit glutathione synthesis, while in vitro studies have shown that chronic low-dose arsenic exposure can activate the p38/Nrf2 pathway, upregulate GCLC expression, and promote glutathione synthesis.

Effect of hesperidin on fluoride-induced neurobehavioral and biochemical changes in rats

Fluoride is the second largest contaminant of drinking water. Fluoride toxicity is a major concern in the endemic areas where a high amount of fluoride is present in ground water. Oxidative stress has been proposed to be one of the mechanisms of fluoride-induced toxicity. Antioxidant-rich food has been found to alleviate fluoride-induced toxicity. Therefore, in this study, we have examined the effect of hesperidin on fluoride-induced neurobehavioral changes in rats. In the current study, male Sprague-Dawley rats were exposed to sodium fluoride through drinking water (120 ppm). Hesperidin (200 mg kg^-1  d^-1 ; per os) was administered either alone or in combination with fluoride-containing drinking water. Bisphinol A diglycidyl ether (BADGE) was used as peroxisome proliferator-activated receptor-γ (PPAR-γ) antagonist and was administered (10 mg kg^-1  d^-1 ; intraperitoneal injection) with/without hesperidin along with fluoride-containing drinking water. The behavioral changes in the animals were assessed by analyzing rotarod test, novel object recognition test, and forced swim test (FST). After 8 weeks, animals were killed to isolate blood and brain for monitoring biochemical changes. The 8-week exposure of fluoride resulted in motor impairment as observed with reduced fall time in rotarod test, memory impairment as observed with reduced preference index in novel object recognition test, and depression-like behavior as observed with reduced mobility index in the FST. Treatment with hesperidin improved neurobehavioral impairment along with restoration in brain biochemical changes (ie, acetylcholinesterase activity and antioxidant and oxidative stress parameters). The protective effect of hesperidin was reversed by coadministration of BADGE. The neuroprotective effect of hesperidin appears to be contributed through PPAR-γ receptor.

Inorganic fluoride and functions of brain

Although actively disputed and questioned, it has been proposed that chronic exposure to inorganic fluoride (F^-) is toxic for brain. The major question for this review was whether an excessive F^- intake is causally related to adverse neurological and cognitive health conditions in human beings and animals. The paper systematically and critically summarizes the findings of the studies showing positive associations between F^- intoxication and various intellectual defects, as well as of those which attempted to clarify the nature of F^- neurotoxicity. Many works provide support for a link between pre- and postnatal F^- exposure and structural and functional changes in the central nervous system responsible for neurological and cognitive disorders. The mechanisms suggested to underlie F^- neurotoxicity include the disturbances in synaptic transmission and synaptic plasticity, premature death of neurons, altered activities of components of intracellular signaling cascades, impaired protein synthesis, deficit of neurotrophic and transcriptional factors, oxidative stress, metabolic changes, inflammatory processes. However, the majority of works have been performed on laboratory rodents using such F^- doses which are never exist in the nature even in the regions of endemic fluorosis. Thus, this kind of treatment is hardly comparable with human exposure even taking into account the higher rate of F^- clearance in animals. Of special importance are the data collected on humans chronically consuming excessive F^- doses in the regions of endemic fluorosis or contacting with toxic F^- compounds at industrial sites, but those works are scarce and often criticized due to low quality. New, expertly performed studies with repeated exposure assessment in independent populations are needed to prove an ability of F^- to impair neurological and intellectual development of human beings and to understand the molecular mechanisms implicated in F^--induced neurotoxicity.

Environmental exposure of arsenic and fluoride and their combined toxicity: A recent update

Environmental exposure to arsenic (As) and fluoride (F) in the recent year has been increased because of excessive use of naturally contaminated ground water. Surface water is also regularly contaminated with these elements in various industrial areas. Arsenicosis and fluorosis upon individual exposure of As and F are reported in many studies. A syndrome of endemic As poisoning and fluorosis occurs during concurrent exposure of As and F. Previous reports showed synergistic, antagonistic and independent effects of these two compounds, although few recent reports also revealed antagonistic effects after co-exposure. Interaction during intestinal absorption and influence of F on As metabolism might be the cause of antagonism. The synergism/antagonism is thought to depend on the dose and duration of the co-exposure. However, the detailed mechanism is still not fully understood and needs further studies. Removal technologies of As and F from contaminated water is available but removal of such contaminants from food is yet to be developed. Antioxidants are useful to mitigate the toxic effects of As and F. This review focused on the effect of co-exposure, amelioration as well as removal techniques of As and F.

Deregulation of autophagy is involved in nephrotoxicity of arsenite and fluoride exposure during gestation to puberty in rat offspring

Exposure to fluoride (F) or arsenite (As) through contaminated drinking water has been associated with chronic nephrotoxicity in humans. Autophagy is a regulated mechanism ubiquitous for the body in a toxic environment with F and As, but the underlying mechanisms of autophagy in the single or combined nephrotoxicity of F and As are unclear. In the present study, we established a rat model of prenatal and postnatal exposure to F and As with the aim of investigating the mechanism underlying nephrotoxicity of these pollutants in offspring. Rats were randomly divided into four groups that received NaF (100 mg/L), NaAsO₂ (50 mg/L), or NaF (100 mg/L) with NaAsO₂ (50 mg/L) in drinking water or clean water during pregnancy and lactation; after weaning, pups were exposed to the same treatment as their mothers until puberty. The results revealed that F and As exposure (alone or combined) led to significant increases of arsenic and fluoride levels in blood and bone, respectively. In this context, F and/or As disrupted histopathology and ultrastructure in the kidney, and also altered creatinine (CRE), urea nitrogen (BUN) and uric acid (UA) levels. Intriguingly, F and/or As uptake induced the formation of autophagosomes in kidney tissue and resulted in the upregulation of genes encoding autophagy-related proteins. Collectively, these results suggest that nephrotoxicity of F and As for offspring exposed to the pollutants from in utero to puberty is associated with deregulation of autophagy and there is an antagonism between F and As in the toxicity autophagy process.

High fat diet deteriorates the memory impairment induced by arsenic in mice: a sub chronic in vivo study

Both arsenic (As) and obesity are associated with brain disorders. However, long term studies to evaluate their concomitant adverse effects on the brain functions are lacking. Present study was conducted to evaluate the long term co-exposure of As and high fat diet (HFD) on memory and brain mitochondrial function in mice. Male mice were randomly divided into 7 groups fed with HFD or ordinary diet (OD) and instantaneously exposed to As (25 or 50 ppm) in drinking water for, 4, 8, 12, 16 or 20 weeks. Step-down passive avoidance method was used for memory assessment and post exposure various parameters including mitochondrial damage, level of reactive oxygen species (ROS), malondialdeid (MDA) and glutathione (GSH) were determined. Results indicated that the retention latency decreased in As (25 and 50 ppm) and HFD received mice after 12 and 16 weeks respectively. Same results were observed at significantly shorter duration (8th week) when As was administered along with HFD as compared to control group. In the HFD alone fed mice increased the mitochondrial membrane damage, levels of ROS and MDA were observed while GSH contents decreased significantly. Concomitant administration of HFD and As amplified those mentioned toxic effects (p < 0.001). In conclusion, our findings demonstrated that the simultaneous HFD and As impaired memory at least three times more than exposing each one alone. These toxic effects could be due to the mitochondria originated oxidative stress along with the depleted antioxidant capacity of the brain of mice.

m6A Demethylase FTO Regulates Dopaminergic Neurotransmission Deficits Caused by Arsenite

Arsenite exposure is known to increase the risk of neurological disorders via alteration of dopamine content, but the detailed molecular mechanisms remain largely unknown. In this study, using both dopaminergic neurons of the PC-12 cell line and C57BL/6J mice as in vitro and in vivo models, our results demonstrated that 6 months of arsenite exposure via drinking water caused significant learning and memory impairment, anxiety-like behavior and alterations in conditioned avoidance and escape responses in male adult mice. We also were the first to reveal that the reduction in dopamine content induced by arsenite mainly resulted from deficits in dopaminergic neurotransmission in the synaptic cleft. The reversible N6- methyladenosine (m6A) modification is a novel epigenetic marker with broad roles in fundamental biological processes. We further evaluated the effect of arsenite on the m6A modification and tested if regulation of the m6A modification by demethylase fat mass and obesity-associated (FTO) could affect dopaminergic neurotransmission. Our data demonstrated for the first time that arsenite remarkably increased m6A modification, and FTO possessed the ability to alleviate the deficits in dopaminergic neurotransmission in response to arsenite exposure. Our findings not only provide valuable insight into the molecular neurotoxic pathogenesis of arsenite exposure, but are also the first evidence that regulation of FTO may be considered as a novel strategy for the prevention of arsenite-associated neurological disorders.

Combination therapy with vitamin C and DMSA for arsenic-fluoride co-exposure in rats

INTRODUCTION

Arsenic and fluoride are recognized globally as the most serious inorganic contaminants in drinking water. As there is no safe and effective treatment for the cases of fluoride poisoning and combined arsenic-fluoride toxicity, the present study was planned to assess (i) the mechanism of combined exposure to arsenic and fluoride via biochemical and spectroscopic data; (ii) the effect of a thiol chelating agent, meso-2,3-dimercaptosuccinic acid (DMSA), either individually or in combination with the antioxidant vitamin C in reversing arsenic-fluoride toxicity; and (iii) whether combination therapy enhances arsenic and fluoride removal from blood and soft tissues.

METHODS

Rats were exposed to arsenic (50 mg l-1) and fluoride (50 mg l-1) individually and in combination for 9 months and later administered DMSA (50 mg kg-1) via an i.p. route and vitamin C (25 mg kg-1) orally for 5 days. Biochemical parameters suggestive of alterations in the heme synthesis pathway, oxidative stress in blood, the liver and the kidneys, and concentrations of arsenic and fluoride in blood and soft tissues were studied. We also studied the infrared (IR) spectra of DNA extracted from the livers and kidneys of the normal and exposed animals.

RESULTS

It was found that chronic arsenic and fluoride exposure led to an increased oxidative stress condition and impaired heme synthesis (67% inhibition in δ-aminolevulinic acid dehydratase activity and 38% increase in δ-aminolevulinic acid synthetase activity). The decreased antioxidant defense mechanism was marked by a 2.25 fold increased concentration of Reactive Oxygen Species (ROS) and a 28% decrease in the Glutathione (GSH) level. Interestingly, concomitant exposure to arsenic and fluoride did not lead to antagonistic effects as the toxic effects were the same as those seen during the individual exposure to both the toxicants. It suggests that toxicity depends on the dose and duration of exposure. Combination therapy with DMSA and vitamin C showed a better efficacy than monotherapy in terms of reducing the arsenic and fluoride burden (more than 70% in blood and soft tissues) as well as reversal in the altered biochemical variables indicative of oxidative stress and tissue damage (80-85%). The infrared (IR) spectra of DNA isolated from the liver and kidneys suggested that the treatment with vitamin C and DMSA had no beneficial effects in terms of reversing DNA damage.

CONCLUSION

On the basis of the above observations, we suggest that the combinational therapy of DMSA and vitamin C would be more effective in arsenic and/or fluoride toxicity; however, more detailed studies are required to address recoveries in DNA damage.

Effects of Perinatal Fluoride Exposure on Short- and Long-Term Memory, Brain Antioxidant Status, and Glutamate Metabolism of Young Rat Pups

Exposure to fluoride (F) during the development affects central nervous system of the offspring rats which results in the impairment of cognitive functions. However, the exact mechanisms of F neurotoxicity are not clearly defined. To investigate the effects of perinatal F exposure on memory ability of young rat offspring, dams were exposed to 5 and 10 mg/L F during gestation and lactation. Additionally, we evaluated the possible underlying neurotoxic mechanisms implicated. The results showed that the memory ability declined in 45-day-old offspring, together with a decrease of catalase and glutamate transaminases activity in specific brain areas. The present study reveals that exposure to F in early stages of rat development leads to impairment of memory in young offspring, highlighting the alterations of oxidative stress markers as well as the activity of enzymes involved in the glutamatergic system as a possible mechanisms of neurotoxicity.

Prevention of Deficit in Neuropsychiatric Disorders through Monitoring of Arsenic and Its Derivatives as Well as Through Bioinformatics and Cheminformatics

Neuropsychiatric disorders are induced by various risk factors, including direct exposure to environmental chemicals. Arsenic exposure induces neurodegeneration and severe psychiatric disorders, but the molecular mechanisms by which brain damage is induced are not yet elucidated. Our aim is to better understand the molecular mechanisms of arsenic toxicity in the brain and to elucidate possible ways to prevent arsenic neurotoxicity, by reviewing significant experimental, bioinformatics, and cheminformatics studies. Brain damage induced by arsenic exposure is discussed taking in account: the correlation between neuropsychiatric disorders and the presence of arsenic and its derivatives in the brain; possible molecular mechanisms by which arsenic induces disturbances of cognitive and behavioral human functions; and arsenic influence during psychiatric treatments. Additionally, we present bioinformatics and cheminformatics tools used for studying brain toxicity of arsenic and its derivatives, new nanoparticles used as arsenic delivery systems into the human body, and experimental ways to prevent arsenic contamination by its removal from water. The main aim of the present paper is to correlate bioinformatics, cheminformatics, and experimental information on the molecular mechanism of cerebral damage induced by exposure to arsenic, and to elucidate more efficient methods used to reduce its toxicity in real groundwater.

Gas chromatography-mass spectrometry based metabolomics profile of hippocampus and cerebellum in mice after chronic arsenic exposure

Intake of arsenic (As) via drinking water has been a serious threat to global public health. Though there are numerous reports of As neurotoxicity, its pathogenesis mechanisms remain vague especially its chronic effects on metabolic network. Hippocampus is a renowned area in relation to learning and memory, whilst recently, cerebellum is argued to be involved with process of cognition. Therefore, the study aimed to explore metabolomics alternations in these two areas after chronic As exposure, with the purpose of further illustrating details of As neurotoxicity. Twelve 3-week-old male C57BL/6J mice were divided into two groups, receiving deionized drinking water (control group) or 50 mg/L of sodium arsenite (via drinking water) for 24 weeks. Learning and memory abilities were tested by Morris water maze (MWM) test. Pathological and morphological changes of hippocampus and cerebellum were captured via transmission electron microscopy (TEM). Metabolic alterations were analyzed by gas chromatography-mass spectrometry (GC-MS). MWM test confirmed impairments of learning and memory abilities of mice after chronic As exposure. Metabolomics identifications indicated that tyrosine increased and aspartic acid (Asp) decreased simultaneously in both hippocampus and cerebellum. Intermediates (succinic acid) and indirect involved components of tricarboxylic acid cycle (proline, cysteine, and alanine) were found declined in cerebellum, indicating disordered energy metabolism. Our findings suggest that these metabolite alterations are related to As-induced disorders of amino acids and energy metabolism, which might therefore, play an important part in mechanisms of As neurotoxicity.

Perinatal Exposure to Arsenic in Drinking Water Alters Glutamatergic Neurotransmission in the Striatum of C57BL/6 Mice

Although exposure to arsenic (As) induces developmental neurotoxicity, there is a lack of data regarding its specific effects on glutamatergic neurotransmission in offspring from dams exposed to As during gestation and lactation. In this study, the body weight, glutamate content, and expression of vesicular glutamate transporter 2 (VGLUT2) and metabotropic glutamate receptors mGluR2 and mGluR3 was examined in the striatum of offspring following treatment of the dams with As (10 or 100 mg/L NaAsO₂ in drinking water). At postnatal day 21, body weight was decreased significantly, whereas the glutamate content in the striatum of offspring in the 100-mg/L As group were not significantly different from those in the control group. Although mGluR3 expression was not significantly different, VGLUT2 and mGluR2 expression was significantly lower in the striatum of offspring of As-exposed dams. These data indicate that altered glutamatergic neurotransmission may contribute to As-induced developmental neurotoxic effects.

Effects of developmental arsenite exposure on hippocampal synapses in mouse offspring

arsenite. The thickness of the postsynaptic density (PSD) decreased, whereas the width of the synaptic cleft widened significantly in arsenite exposure groups. Moreover, protein expression of both PSD-95 and SYP decreased significantly in arsenite exposure groups. In conclusion, the results of this study demonstrated that developmental arsenite exposure could depress the expression of synaptic proteins, subsequently cause alteration in synaptic structures, and finally contribute to arsenite-induced deficits in spatial learning and memory ability in mouse offspring.

An Evaluation of Neurotoxicity Following Fluoride Exposure from Gestational Through Adult Ages in Long-Evans Hooded Rats

At elevated levels, fluoride (F^-) exposure has been associated with adverse human health effects. In rodents, F^- exposure has been reported to induce deficits in motor performance and learning and memory. In this study, we examined Long-Evans hooded male rats maintained on a standard diet (20.5 ppm F^-) or a low F^- diet (3.24 ppm F^-) with drinking water exposure to 0, 10, or 20 ppm F^- from gestational day 6 through adulthood. At postnatal day 25, brain F^- levels were 0.048 or 0.081 μg/g and femur 235 or 379.8 μg/g for 10 and 20 ppm F^-, respectively. Levels increase with age and in adults, levels for plasma were 0.036 or 0.025 μg/ml; for the brain 0.266 or 0.850 μg/g; and for the femur, 681.2 or 993.4 μg/g. At these exposure levels, we observed no exposure-related differences in motor, sensory, or learning and memory performance on running wheel, open-field activity, light/dark place preference, elevated plus maze, pre-pulse startle inhibition, passive avoidance, hot-plate latency, Morris water maze acquisition, probe test, reversal learning, and Y-maze. Serum triiodothyronine (T3), thyroxine (T4), and thyroid stimulating hormone (TSH) levels were not altered as a function of 10 or 20 ppm F^- in the drinking water. No exposure-related pathology was observed in the heart, liver, kidney, testes, seminal vesicles, or epididymides. Mild inflammation in the prostate gland was observed at 20 ppm F^-. No evidence of neuronal death or glial activation was observed in the hippocampus at 20 ppm F^-.

Excessive ER stress and the resulting autophagic flux dysfunction contribute to fluoride-induced neurotoxicity

Fluoride is capable of inducing neurotoxicity, but its mechanisms remain elusive. This study aimed to explore the roles of endoplasmic reticulum (ER) stress and autophagy in sodium fluoride (NaF)-induced neurotoxicity, focusing on the regulating role of ER stress in autophagy. The in vivo results demonstrated that NaF exposure impaired the learning and memory capabilities of rats, and resulted in histological and ultrastructural abnormalities in rat hippocampus. Moreover, NaF exposure induced excessive ER stress and associated apoptosis, as manifested by elevated IRE1α, GRP78, cleaved caspase-12 and cleaved-caspase-3, as well as defective autophagy, as shown by increased Beclin1, LC3-II and p62 expression in hippocampus. Consistently, the in vitro results further verified the findings of in vivo study that NaF induced excessive ER stress and defective autophagy in SH-SY5Y cells. Notably, inhibition of autophagy in NaF-treated SH-SY5Y cells with Wortmannin or Chloroquine decreased, while induction of autophagy by Rapamycin increased the cell viability. These results were correlated well with the immunofluorescence observations, thus confirming the pivotal role of autophagic flux dysfunction in NaF-induced cell death. Importantly, mitigation of ER stress by 4-phenylbutyrate in NaF-treated SH-SY5Y cells inhibited the expressions of autophagy markers, and decreased cell apoptosis. Taken together, these data suggest that neuronal death resulted from excessive ER stress and autophagic flux dysfunction contributes to fluoride-elicited neurotoxicity. Moreover, the autophagic flux dysfunction was mediated by excessive ER stress, which provided novel insight into a better understanding of fluoride-induced neurotoxicity.

Biomarkers of chronic fluoride exposure in groundwater in a highly exposed population

This study examined the relation between fluoride (F-) concentrations in fingernail clippings and urine and the prevalence and severity of enamel fluorosis (EF) among Ethiopian Rift Valley populations exposed to high levels of F- in drinking water. The utility of fingernail clippings as a biomarker for F- exposure and EF was also assessed for the first time in a high-F- region. The study recorded the EF status of 386 individuals (10 to 50years old), who consume naturally contaminated groundwater with widely varying F- concentration (0.6-15mg/L). The mean F- concentrations among residents of communities with primary reliance on groundwater were 5.1mg/kg (range: 0.5-34mg/kg) in fingernails and 8.9mg/L (range: 0.44-34mg/L) in urine. We show strong positive correlations between F- in drinking water and 12-hour urinary excretion (r=0.74, p<0.001, n=287), fingernail F- content (r=0.6, p<0.001, n=258), and mean individual measures of EF severity as measured using the Thylstrup and Fejerskov (TF) Index (r=0.42, p<0.001, n=316). The data indicate that both fingernail and urine measures are good biomarkers for F- exposure and EF outcomes, the latter being slightly more sensitive. Cases of moderate/severe EF were significantly more common among younger subjects (10 to 15years old) than older subjects (mostly >25years old) (p<0.001), consistent with their greater exposure to F- during early childhood, which is the only period of life the enamel is at risk of fluorosis. In this younger population, EF may be useful as a biomarker for identifying individuals with other potential health effects that depend on a specific age window of susceptibility. The finding of exceptionally high F- concentrations in water, fingernail clippings and urine in this region should motivate further investigations of other potential health consequences such as bone disease and abnormalities in the function of the neurological and endocrine systems.

Heteromeric channels formed by TRPC1, TRPC4 and TRPC5 define hippocampal synaptic transmission and working memory

Canonical transient receptor potential (TRPC) channels influence various neuronal functions. Using quantitative high-resolution mass spectrometry, we demonstrate that TRPC1, TRPC4, and TRPC5 assemble into heteromultimers with each other, but not with other TRP family members in the mouse brain and hippocampus. In hippocampal neurons from Trpc1/Trpc4/Trpc5-triple-knockout (Trpc1/4/5^-/-) mice, lacking any TRPC1-, TRPC4-, or TRPC5-containing channels, action potential-triggered excitatory postsynaptic currents (EPSCs) were significantly reduced, whereas frequency, amplitude, and kinetics of quantal miniature EPSC signaling remained unchanged. Likewise, evoked postsynaptic responses in hippocampal slice recordings and transient potentiation after tetanic stimulation were decreased. In vivo, Trpc1/4/5^-/- mice displayed impaired cross-frequency coupling in hippocampal networks and deficits in spatial working memory, while spatial reference memory was unaltered. Trpc1/4/5^-/- animals also exhibited deficiencies in adapting to a new challenge in a relearning task. Our results indicate the contribution of heteromultimeric channels from TRPC1, TRPC4, and TRPC5 subunits to the regulation of mechanisms underlying spatial working memory and flexible relearning by facilitating proper synaptic transmission in hippocampal neurons.

The Influence of Fluorine on the Disturbances of Homeostasis in the Central Nervous System

Fluorides occur naturally in the environment, the daily exposure of human organism to fluorine mainly depends on the intake of this element with drinking water and it is connected with the geographical region. In some countries, we can observe the endemic fluorosis-the damage of hard and soft tissues caused by the excessive intake of fluorine. Recent studies showed that fluorine is toxic to the central nervous system (CNS). There are several known mechanisms which lead to structural brain damage caused by the excessive intake of fluorine. This element is able to cross the blood-brain barrier, and it accumulates in neurons affecting cytological changes, cell activity and ion transport (e.g. chlorine transport). Additionally, fluorine changes the concentration of non-enzymatic advanced glycation end products (AGEs), the metabolism of neurotransmitters (influencing mainly glutamatergic neurotransmission) and the energy metabolism of neurons by the impaired glucose transporter-GLUT1. It can also change activity and lead to dysfunction of important proteins which are part of the respiratory chain. Fluorine also affects oxidative stress, glial activation and inflammation in the CNS which leads to neurodegeneration. All of those changes lead to abnormal cell differentiation and the activation of apoptosis through the changes in the expression of neural cell adhesion molecules (NCAM), glial fibrillary acidic protein (GFAP), brain-derived neurotrophic factor (BDNF) and MAP kinases. Excessive exposure to this element can cause harmful effects such as permanent damage of all brain structures, impaired learning ability, memory dysfunction and behavioural problems. This paper provides an overview of the fluoride neurotoxicity in juveniles and adults.