Effects of arsenite on central monoamines and plasmatic levels of adrenocorticotropic hormone (ACTH) in mice

Co-administration of L-Ascorbic Acid and α-Tocopherol Alleviates Arsenic-Induced Immunotoxicities in the Thymus and Spleen by Dwindling Oxidative Stress-Induced Inflammation

Herein, we investigated whether L-ascorbic acid (L-AA) and α-tocopherol (α-T) co-administration has the potential to alleviate arsenic-induced immunotoxicities in the thymus, spleen, and circulating leukocytes. Forty-eight adult male Wistar rats were randomly divided into four groups before the treatment: group I (control); group II (sodium arsenite, 3 mg/kg/day/rat); group III (sodium arsenite + L-AA (200 mg/kg/day/rat) and α-T (400 mg/kg/day/rat)); group IV (L-AA and α-T). The result showed that sodium arsenite exposure (consecutive 30 days) caused weight reduction, structural alterations in the thymus and spleen, accompanied by a decrease in thymocyte and splenocyte count. Decreased superoxide dismutase and catalase activity, increased malondialdehyde and protein-carbonyl content, reduced Nrf2 and Bcl2 expression, and increased p-ERK, NF-kβ, Bax, and cleaved-caspase-3 expression were also observed in the thymus and spleen of arsenic-exposed rats. Enhanced plasma ACTH and corticosterone, ROS-induced apoptosis of lymphocytes were also observed. L-AA and α-T co-administration has the potential to abrogate the deleterious impact of arsenic on the thymus, spleen, and circulating lymphocytes. Whole transcriptome analysis of leukocytes revealed that arsenic treatment augmented the expression of Itga4, Itgam, and MMP9 genes, which might help in transient migration of the leukocytes through the endothelial cell layer. Co-administration with L-AA and α-T maintained Itga4, Itgam, and MMP9 gene expression within leukocytes at a lower level.

Nanoplastics promote arsenic-induced ROS accumulation, mitochondrial damage and disturbances in neurotransmitter metabolism of zebrafish (Danio rerio)

As a carrier, nanoplastics (NPs) can adsorb other toxic substances and thus modify their biological toxicity. Numerous studies have investigated the neurotoxic of high concentrations of arsenic (As, 2.83 mg/L-5 mg/L). However, it is still unknown whether the relatively low environmentally relevant concentrations of As (200 μg/L) can damage the structure and function of fish brains with the presence of NPs. In this study, zebrafish were exposed to polystyrene NPs, As and their mixture for 30 days respectively. Firstly, we found that the presence of NPs promoted the accumulation of As in zebrafish brains. Thereby the co-exposure of NPs and As further promoted the production of reactive oxygen species (ROS) in zebrafish brains compared with the single exposure of NPs or As, resulting in severe oxidative stress. Moreover, accumulated ROS directly damaged the mitochondrial membrane and mtDNA in zebrafish brains. Moreover, the mitochondrial damage was further aggravated due to inhibited mitochondrial fusion and activated mitochondrial division and mitophagy. Ultimately, the co-exposure led to mitochondrial damage in the zebrafish brain. Damaged mitochondria may not meet the high energy metabolic requirement for neuronal function. As a result, the normal function of nerve cells was adversely affected and eventually cell apoptosis may occur. Besides, the co-exposure caused more significant structural alterations in zebrafish brain tissue. Finally, the co-exposure of NPs and As caused abnormal biosynthesis and degradation of dopamine and acetylcholine. These resulted in decreased dopamine levels and increased acetylcholine levels in zebrafish brains. In conclusion, the presence of NPs promoted the accumulation of As, thereby inducing severe oxidative stress, which caused structural alterations and mitochondrial damage in the zebrafish brain, thus disordering neuromodulation, which may ultimately cause neurological dysfunction in zebrafish. This study will provide a risk assessment for evaluating the biotoxicity of NPs and As to fish and even other animals.

Lipid Metabolism Alterations in a Rat Model of Chronic and Intergenerational Exposure to Arsenic

Chronic exposure to arsenic (As), whether directly through the consumption of contaminated drinking water or indirectly through the daily intake of As-contaminated food, is a health threat for more than 150 million people worldwide. Epidemiological studies found an association between chronic consumption of As and several pathologies, the most common being cancer-related disorders. However, As consumption has also been associated with metabolic disorders that could lead to diverse pathologies, such as type 2 diabetes mellitus, nonalcoholic fatty liver disease, and obesity. Here, we used ultra-performance liquid chromatography (UPLC) coupled to electrospray ionization/quadrupole time-of-flight mass spectrometry (ESI-QToF) to assess the effect of chronic intergenerational As exposure on the lipid metabolism profiles of serum from 4-month-old Wistar rats exposed to As prenatally and also during early life in drinking water (3 ppm). Significant differences in the levels of certain identified lysophospholipids, phosphatidylcholines, and triglycerides were found between the exposed rats and the control groups, as well as between the sexes. Significantly increased lipid oxidation determined by the malondialdehyde (MDA) method was found in exposed rats compared with controls. Chronic intergenerational As exposure alters the rat lipidome, increases lipid oxidation, and dysregulates metabolic pathways, the factors associated with the chronic inflammation present in different diseases associated with chronic exposure to As (i.e., keratosis, Bowen's disease, and kidney, liver, bladder, and lung cancer).

Influence of age on arsenic-induced behavioral and cholinergic perturbations: Amelioration with zinc and α-tocopherol

This study was planned to determine arsenic (As) (10 mg/kg body weight given through oral gavage) induced behavioral and cholinergic perturbations in three different age groups of rats; young (postnatal day 21), adult (3 months), and aged (18 months) at 7 days post-acute exposure ( n = 6 for each of the four groups of all three age points). Further, we also evaluated the ameliorative effect of essential metal zinc (Zn; 0.02% through drinking water) and an antioxidant, α-tocopherol (vitamin E; 125 mg/kg body weight through oral gavage) against As-induced neurotoxicity. As exposure showed significant alterations in behavioral functions (open-field behavior, total locomotor activity, grip strength, exploratory behavior, and water maze learning). Cholinergic studies in three brain regions (cerebral cortex, cerebellum, and hippocampus) of different age groups also showed significant increase in acetylcholine levels and a decrease in acetylcholinesterase activity. These effects were more pronounced in hippocampus followed by cerebral cortex and cerebellum. Among the three different age points, aged animals were found to be more vulnerable to the As-induced toxicity as compared to young and adult animals suggesting that As neurotoxicity is age dependent. These As-induced alterations were significantly reversed following supplementation with Zn or vitamin E. However, vitamin E was found to elicit greater protection as compared to Zn in restoring the altered behavioral and cholinergic perturbations, providing evidence for As-induced oxidative damage.

In Vivo and In Vitro Arsenic Exposition Induces Oxidative Stress in Anterior Pituitary Gland

Inorganic arsenic (iAs) is at the top of toxic metalloids. Inorganic arsenic-contaminated water consumption is one of the greatest environmental health threats worldwide. Human iAs exposure has been associated with cancers of several organs, neurological disorders, and reproductive problems. Nevertheless, there are no reports describing how iAs affects the anterior pituitary gland. The aim of this study was to investigate the mechanisms involved in iAs-mediated anterior pituitary toxicity both in vivo and in vitro. We showed that iAs administration (from 5 to 100 ppm) to male rats through drinking water increased messenger RNA expression of several oxidative stress-responsive genes in the anterior pituitary gland. Serum prolactin levels diminished, whereas luteinizing hormone (LH) levels were only affected at the higher dose tested. In anterior pituitary cells in culture, 25 µmol/L iAs significantly decreased prolactin release in a time-dependent fashion, whereas LH levels remained unaltered. Cell viability was significantly reduced mainly by apoptosis evidenced by morphological and phosphatidylserine externalization studies. This process is characterized by early depolarization of mitochondrial membrane potential and increased levels of reactive oxygen species. Expression of some key oxidative stress-responsive genes, such as heme oxygenase-1 and metallothionein-1, was also stimulated by iAs exposure. The antioxidant N-acetyl cysteine prevented iAs-induced effects on the expression of oxidative stress markers, prolactin release, and apoptosis. In summary, the present work demonstrates for the first time that iAs reduces prolactin release both in vivo and in vitro and induces apoptosis in anterior pituitary cells, possibly resulting from imbalanced cellular redox status.

Platelet hyperactivity, neurobehavioral symptoms and depression among Indian women chronically exposed to low level of arsenic

The prevalence of neurobehavioral symptoms (NBS) and depression has been investigated in premenopausal rural women of West Bengal, India enrolled from arsenic (As) endemic (groundwater As 11-50 μg/L; n = 342) and control areas (As level ≤ 10 μg/L; n = 312). The subjective symptoms questionnaire and Beck's 21-point depression inventory-II were used for the detection of NBS and depression, respectively. Platelet P-selectin expression was measured by flow cytometry, plasma neurotransmitter activity with high performance liquid chromatography and groundwater As level by atomic absorption spectroscopy. The As level in groundwater was 2.72 ± 1.18 μg/L in control and 28.3 ± 13.51 μg/L in endemic areas (p < 0.0001). Women residing in endemic areas demonstrated a higher prevalence of depressive symptoms (39.8 vs. 19.9%, p < 0.001) and anxiety (43.3 vs. 18.0% in control, p < 0.001), fatigue (68.4 vs. 23.4%, p < 0.0001), reduced sense of taste (15.8 vs. 4.5%, p<0.0001) and smell (14.9 vs. 5.8%, p < 0.001); burning sensation (36.8 vs. 5.4%, p < 0.0001) and tingling or numbness in the extremities (25.1 vs. 5.1%, p < 0.0001); and transient loss of memory (69.9 vs. 28.2%, p < 0.001). As-exposed women had 1.6-times more plasma epinephrine and norepinephrine (p < 0.05), 1.8-times higher level plasma serotonin with 28.9% lower intraplatelet serotonin (p < 0.05 for both), but their plasma dopamine level was not significantly different (p>0.05) from that of controls. Moreover, women from endemic areas had 2.3-times more P-selectin-expressing platelets in their circulation (p < 0.001). After controlling the potential confounders, chronic low level As (11-50 μg/L) exposure showed a positive association with the prevalence of neurobehavioral symptoms and depression among Indian women in their child-bearing age.

Arsenic decreases antinociceptive activity of paracetamol: possible involvement of serotonergic and endocannabinoid receptors

We assessed whether repeated arsenic exposure can decrease paracetamol-mediated antinociception by modulating serotonergic and endocannabinoid pathways. Rats were preexposed to elemental arsenic (4ppm) as sodium arsenite through drinking water for 28 days. Next day paracetamol's (400mg/kg, oral) antinociceptive activity was assessed through formalin-induced nociception. Serotonin content and gene expression of 5-HT1A, 5-HT2A and CB1 receptors were evaluated in brainstem and frontal cortex. Arsenic decreased paracetamol-mediated analgesia. Paracetamol, but not arsenic, increased serotonin content in these regions. Arsenic attenuated paracetamol-mediated increase in serotonin level. Paracetamol did not alter 5-HT1A expression, but caused down-regulation of 5-HT2A and up-regulation of CB1 receptors. Arsenic down-regulated these receptors. However, paracetamol-mediated down-regulation of 5-HT2A was more pronounced. Arsenic did not modify paracetamol's effect on 5-HT1A expression, but reduced paracetamol-mediated down-regulation of 5-HT2A and reversed up-regulation of CB1 receptors. Results suggest arsenic reduced paracetamol-induced analgesia possibly by interfering with pronociceptive 5-HT2A and antinociceptive CB1 receptors.

Arsenic affects on cerebellar development of mice

To evaluate arsenic affects on the development of cerebellum, the mother mice received drinking water containing arsenic trioxide (As2O3) 4 ppm during gestation and lactation period. The cytogenesis was observed by immunohistochemical technique using 5'-bromo-2'-deoxyuridine (BrdU) antibody. To characterize the arsenic neurotoxicity, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), an oxidative DNA lesion marker, and 8-nitroguanine, a nitrative DNA lesion marker were used to verify DNA damage. Arsenic-exposed litters showed neuron necrosis. The mitosis of granule cells decreased dramatically in arsenic-exposed mice as compared with arsenic unexposed mice. 8-OxodG was formed in neurons of all the layers, especially in the granular layer in cerebellum of arsenic-exposed mice. There is no significant difference, however, in the expression of 8-nitroguanine between arsenic-exposed and -unexposed mice. These results indicate that arsenic can disturb the mitosis of granule cells and interfere with the normal development of mice cerebellum. Arsenic-induced pathological changes in vivo may be caused by oxidative DNA damage other than nitrative DNA damage.

Monoisoamyl 2,3-dimercaptosuccinic acid attenuates arsenic induced toxicity: behavioral and neurochemical approach

Chronic exposure to arsenic in drinking water is associated with skin lesions, neurological effects, hypertension and high risk of cancer. The treatment in use at present employs administration of thiol chelators, such as meso-2,3-dimercaptosuccinic acid (DMSA) which are compromised with number of limitations due to their lipophobic nature. To address this problem, therapeutic efficacy of monoisoamyl meso-2,3-dimercaptosuccinic acid (MiADMSA), an analog of DMSA having lipophilic character, was examined against chronic arsenic poisoning in rats. Adult male Wistar rats were orally exposed to arsenic (2mg sodium arsenite/kg body weight) for 10 weeks followed by treatment with MiADMSA (50mg/kg, orally, once daily for 5 consecutive days). As-exposed rats showed significant differences in behavioral functions (open field behavior, total locomotor activity, grip strength and exploratory behavior) and water maze learning. Further, the biochemical studies performed on three brain regions (cerebellum, cortex and hippocampus) also showed significant elevation in malondialdehyde (MDA) levels with a concomitant decrease in the oxidative stress marker enzymes Mn-superoxide dismutase (Mn-SOD), Cu/Zn-superoxide dismutase (Cu/Zn-SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST). The alterations were more pronounced in cortex compared to cerebellum and hippocampus. The results showed that MiADMSA significantly reversed the As-induced alterations in behavior and biochemical variables suggestive of oxidative injury.

Protective effect of taurine on the decreased biogenic amine neurotransmitter levels in the brain of mice exposed to arsenic

Arsenic (As) exposure has a toxic effect on the central nervous system, especially on learning and memory. Norepinephrine (NE), dopamine (DA), and serotonin (5-HT) play an important role in learning and memory function of the brain. In the present study, the protective effect of taurine on the disturbed biogenic amine neurotransmitter levels in the mouse brain induced by arsenic was examined. Sixty SPF mice were divided into three groups. The As exposure group was administered with 4 ppm As(2)O(3) through drinking water for 60 days. The protective group was treated with both 4 ppm As(2)O(3) and 150 mg/kg taurine. The control group was given drinking water alone. The levels of NE, DA, and 5-HT were determined by HPLC in the cerebrum and cerebellum of mice. Ultrastructure of synapses in brain tissue of mice was observed in these groups by transmission electron microscopy. The mRNA expressions of dopamine beta hydroxylase (DBH), tyrosine hydroxylase (TH), and tryptophan hydroxylase (TPH) as NE, DA, and 5-HT synzymes were also analyzed by real-time RT-PCR. The results showed that the concentrations of NE, DA, and 5-HT; the number of synaptic vesicles; and the expressions of TH, TPH, and DBH genes in the brains of mice exposed to As alone were significantly decreased. However, administration of taurine significantly alleviated the toxic effect on biochemicals detected in the experiment, compared with that in the brain of mice exposed to As alone. These results indicated that taurine was effective in counteracting the decreased biogenic amine neurotransmitter level and the mRNA expressions of their synzymes induced by arsenic.

Perinatal exposure to 50 ppb sodium arsenate induces hypothalamic-pituitary-adrenal axis dysregulation in male C57BL/6 mice

Over the past two decades, key advancements have been made in understanding the complex pathology that occurs following not only high levels of arsenic exposure (>1 ppm) but also levels previously considered to be low (<100 ppb). Past studies have characterized the deleterious effects of arsenic on the various functions of cardiovascular, pulmonary, immunological, respiratory, endocrine and neurological systems. Other research has demonstrated an elevated risk of a multitude of cancers and increased rates of psychopathology, even at very low levels of arsenic exposure. The hypothalamic-pituitary-adrenal (HPA) axis represents a multisite integration center that regulates a wide scope of biological and physiological processes: breakdown within this system can generate an array of far-reaching effects, making it an intriguing candidate for arsenic-mediated damage. Using a mouse model, we examined the effects of perinatal exposure to 50 ppb sodium arsenate on the functioning of the HPA axis through the assessment of corticotrophin-releasing factor (CRF), proopiomelanocortin (Pomc) mRNA, adrenocorticotrophin hormone (ACTH), corticosterone (CORT), 11β-hydroxysteroid dehydrogenase Type 1 (11β-HSD 1), and glucocorticoid receptor (GR) protein and mRNA. Compared to controls, we observed that the perinatal arsenic-exposed offspring exhibit an increase in hypothalamic CRF, altered CORT secretion both at baseline and in response to a stressor, decreased hippocampal 11β-HSD 1 and altered subcellular GR distribution in the hypothalamus. These data indicate significant HPA axis impairment at post-natal day 35 resulting from perinatal exposure to 50 ppb sodium arsenate. Our findings suggest that the dysregulation of this critical regulatory axis could underlie important molecular and cognitive pathology observed following exposure to arsenic.

Effects of prenatal exposure to sodium arsenite on motor and food-motivated behaviors from birth to adulthood in C57BL6/J mice

Consumption of arsenic-contaminated drinking water is associated with numerous cancers and dermal and vascular diseases. Arsenic is also a potent nervous system toxicant and epidemiological studies indicate that intellectual functions in children are compromised following early developmental exposure. This study was designed to examine the effects of arsenic on a broad range of age-specific behaviors including basic sensory-motor responses in neonates, locomotor activity and grip strength in juveniles, and operant measures of learning and attention in adults. Pregnant C57BL6/J mice consumed drinking water containing 0, 8, 25, or 80 ppm sodium arsenite from the fourth day of gestation until birth. Arsenic produced a range of behavioral impairments in male and female offspring at each of the test ages. The most striking effects of arsenic were on the development of gait and other motor responses including acoustic startle, righting reflexes, and forelimb grip. These results suggest that developmental arsenic exposure can produce other behavioral impairments in children in addition to cognitive impairment.

Neuroprotective efficacy of curcumin in arsenic induced cholinergic dysfunctions in rats

Our recent studies have shown that curcumin protects arsenic induced neurotoxicity by modulating oxidative stress, neurotransmitter levels and dopaminergic system in rats. As chronic exposure to arsenic has been associated with cognitive deficits in humans, the present study has been carried out to implore the neuroprotective potential of curcumin in arsenic induced cholinergic dysfunctions in rats. Rats treated with arsenic (sodium arsenite, 20mg/kg body weight, p.o., 28 days) exhibited a significant decrease in the learning activity, assessed by passive avoidance response associated with decreased binding of (3)H-QNB, known to label muscarinic-cholinergic receptors in hippocampus (54%) and frontal cortex (27%) as compared to controls. Decrease in the activity of acetylcholinesterase in hippocampus (46%) and frontal cortex (33%), staining of Nissl body, immunoreactivity of choline acetyltransferase (ChAT) and expression of ChAT protein in hippocampal region was also observed in arsenic treated rats as compared to controls. Simultaneous treatment with arsenic and curcumin (100mg/kg body weight, p.o., 28 days) increased learning and memory performance associated with increased binding of (3)H-QNB in hippocampus (54%), frontal cortex (25%) and activity of acetylcholinesterase in hippocampus (41%) and frontal cortex (29%) as compared to arsenic treated rats. Increase in the expression of ChAT protein, immunoreactivity of ChAT and staining of Nissl body in hippocampal region was also observed in rats simultaneously treated with arsenic and curcumin as compared to those treated with arsenic alone. The results of the present study suggest that curcumin significantly modulates arsenic induced cholinergic dysfunctions in brain and also exhibits neuroprotective efficacy of curcumin.

Arsenic affects expression and processing of amyloid precursor protein (APP) in primary neuronal cells overexpressing the Swedish mutation of human APP

Arsenic poisoning due to contaminated water and soil, mining waste, glass manufacture, select agrochemicals, as well as sea food, affects millions of people world wide. Recently, an involvement of arsenic in Alzheimer's disease (AD) has been hypothesized (Gong and O'Bryant, 2010). The present study stresses the hypothesis whether sodium arsenite, and its main metabolite, dimethylarsinic acid (DMA), may affect expression and processing of the amyloid precursor protein (APP), using the cholinergic cell line SN56.B5.G4 and primary neuronal cells overexpressing the Swedish mutation of APP, as experimental approaches. Exposure of cholinergic SN56.B5.G4 cells with either sodium arsenite or DMA decreased cell viability in a concentration- and exposure-time dependent manner, and affected the activities of the cholinergic enzymes acetylcholinesterase and choline acetyltransferase. Both sodium arsenite and DMA exposure of SN56.B5.G4 cells resulted in enhanced level of APP, and sAPP in the membrane and cytosolic fractions, respectively. To reveal any effect of arsenic on APP processing, the amounts of APP cleavage products, sAPPβ, and β-amyloid (Aβ) peptides, released into the culture medium of primary neuronal cells derived from transgenic Tg2576 mice, were assessed by ELISA. Following exposure of neuronal cells by sodium arsenite for 12h, the membrane-bound APP level was enhanced, the amount of sAPPβ released into the culture medium was slightly higher, while the levels of Aβ peptides in the culture medium were considerably lower as compared to that assayed in the absence of any drug. The sodium arsenite-induced reduction of Aβ formation suggests an inhibition of the APP γ-cleavage step by arsenite. In contrast, DMA exposure of neuronal cells considerably increased formation of Aβ and sAPPβ, accompanied by enhanced membrane APP level. The DMA-induced changes in APP processing may be the result of the enhanced APP expression. Alternatively, increased Aβ production may also be due to stimulation of caspase activity by arsenic compounds, or failure in Aβ degradation. In summary, the present report clearly demonstrates that sodium arsenite and DMA affect processing of APP in vitro.

Caenorhabditis elegans bicarbonate transporter ABTS-1 is involved in arsenite toxicity and cholinergic signaling

Arsenic poisoning affects millions of people worldwide. Although there is accumulating evidence to suggest that the nervous system is a target of arsenic, relatively little information is known regarding its effects on the nervous system. The effects of arsenite on the nervous system in Caenorhabditis elegans were investigated in the present study. We found that abts-1, which encodes a Na(+)-dependent Cl(-)/HCO(3)(-) transporter, is required to protect C. elegans from arsenite toxicity. The abts-1::GFP transgene is primarily expressed in neurons and the hypodermis, but stronger expression was also observed in the pharynx and body wall muscle cells after exposure to arsenite. The steady-state level of ABTS-1 mRNA increased in response to arsenite exposure. We showed that worms lacking abts-1 are hypersensitive to the paralytic effects of the cholinesterase inhibitor, aldicarb, and the nicotinic acetylcholine receptor agonist, levamisole. We also showed that arsenite enhanced sensitivity to aldicarb and levamisole in abts-1 mutant worms. Our results indicate neuronal effects of arsenite and the ABTS-1 bicarbonate transporter.

Arsenic species, AS3MT amount, and AS3MT gene expression in different brain regions of mouse exposed to arsenite

Human exposure to inorganic arsenic (iAs) has been associated with cancer and serious injury to various internal organs, as well as peripheral neuropathy, endocrine disruption and diverse effects in the central nervous system (CNS). Using rodent models, it is possible to demonstrate As accumulation in the brain that leads to defects in operant learning, behavioral changes, and affect pituitary gonadotrophins. iAs biomethylation in the CNS is a significant process, yielding products that are more reactive and toxic than the parent compound. Mice received 2.5, 5, and 10 mg/kg/day sodium arsenite orally for 9 days. We investigated the distribution of iAs and its metabolites as well as the mRNA and protein expression of arsenic (III) methyltransferase (AS3MT), which encodes the key enzyme in iAs metabolism, in the cerebral cortex, hippocampus, striatum, mesencephalon, thalamus, cerebellum, hypothalamus, pons, medulla oblongata, and pituitary of mouse brain. Our findings show that methylated As metabolites are present in all brain regions studied suggesting that AS3MT is ubiquitously expressed in the brain and it is not inducible by dose of arsenite. There is also a dose-related accumulation of As species in all brain regions, with the highest accumulation observed in the pituitary. The higher distribution of arsenicals in pituitary can help to explain the neuroendocrine effects associated with iAs exposure.

Analysis of genomic dose-response information on arsenic to inform key events in a mode of action for carcinogenicity

A comprehensive literature search was conducted to identify information on gene expression changes following exposures to inorganic arsenic compounds. This information was organized by compound, exposure, dose/concentration, species, tissue, and cell type. A concentration-related hierarchy of responses was observed, beginning with changes in gene/protein expression associated with adaptive responses (e.g., preinflammatory responses, delay of apoptosis). Between 0.1 and 10 microM, additional gene/protein expression changes related to oxidative stress, proteotoxicity, inflammation, and proliferative signaling occur along with those related to DNA repair, cell cycle G2/M checkpoint control, and induction of apoptosis. At higher concentrations (10-100 microM), changes in apoptotic genes dominate. Comparisons of primary cell results with those obtained from immortalized or tumor-derived cell lines were also evaluated to determine the extent to which similar responses are observed across cell lines. Although immortalized cells appear to respond similarly to primary cells, caution must be exercised in using gene expression data from tumor-derived cell lines, where inactivation or overexpression of key genes (e.g., p53, Bcl-2) may lead to altered genomic responses. Data from acute in vivo exposures are of limited value for evaluating the dose-response for gene expression, because of the transient, variable, and uncertain nature of tissue exposure in these studies. The available in vitro gene expression data, together with information on the metabolism and protein binding of arsenic compounds, provide evidence of a mode of action for inorganic arsenic carcinogenicity involving interactions with critical proteins, such as those involved in DNA repair, overlaid against a background of chemical stress, including proteotoxicity and depletion of nonprotein sulfhydryls. The inhibition of DNA repair under conditions of toxicity and proliferative pressure may compromise the ability of cells to maintain the integrity of their DNA.

Chronic low-level arsenic exposure causes gender-specific alterations in locomotor activity, dopaminergic systems, and thioredoxin expression in mice

Arsenic (As) is a toxic metalloid widely present in the environment. Human exposure to As has been associated with the development of skin and internal organ cancers and cardiovascular disorders, among other diseases. A few studies report decreases in intelligence quotient (IQ), and sensory and motor alterations after chronic As exposure in humans. On the other hand, studies of rodents exposed to high doses of As have found alterations in locomotor activity, brain neurochemistry, behavioral tasks, and oxidative stress. In the present study both male and female C57Bl/6J mice were exposed to environmentally relevant doses of As such as 0.05, 0.5, 5.0, or 50 mg As/L of drinking water for 4 months, and locomotor activity was assessed every month. Male mice presented hyperactivity in the group exposed to 0.5 mg As/L and hypoactivity in the group exposed to 50 mg As/L after 4 months of As exposure, whereas female mice exposed to 0.05, 0.5, and 5.0 mg As/L exhibited hyperactivity in every monthly test during As exposure. Furthermore, striatal and hypothalamic dopamine content was decreased only in female mice. Also decreases in tyrosine hydroxylase (TH) and cytosolic thioredoxin (Trx-1) mRNA expression in striatum and nucleus accumbens were observed in male and female mice, respectively. These results indicate that chronic As exposure leads to gender-dependent alterations in dopaminergic markers and spontaneous locomotor activity, and down-regulation of the antioxidant capacity of the brain.

Moderate perinatal arsenic exposure alters neuroendocrine markers associated with depression and increases depressive-like behaviors in adult mouse offspring

Arsenic is one of the most common heavy metal contaminants found in the environment, particularly in water. We examined the impact of perinatal exposure to relatively low levels of arsenic (50 parts per billion, ppb) on neuroendocrine markers associated with depression and depressive-like behaviors in affected adult C57BL/6J mouse offspring. Whereas most biomedical research on arsenic has focused on its carcinogenic potential, a few studies suggest that arsenic can adversely affect brain development and neural function. Compared to controls, offspring exposed to 50 parts per billion arsenic during the perinatal period had significantly elevated serum corticosterone levels, reduced whole hippocampal CRFR 1 protein level and elevated dorsal hippocampal serotonin 5HT 1A receptor binding and receptor-effector coupling. 5HT 1A receptor binding and receptor-effector coupling were not different in the ventral hippocampal formation, entorhinal or parietal cortices, or inferior colliculus. Perinatal arsenic exposure also significantly increased learned helplessness and measures of immobility in a forced swim task. Taken together, these results suggest that perinatal arsenic exposure may disrupt the regulatory interactions between the hypothalamic-pituitary-adrenal axis and the serotonergic system in the dorsal hippocampal formation in a manner that predisposes affected offspring to depressive-like behavior. These results are the first to demonstrate that relatively low levels of arsenic exposure during development can have long-lasting adverse effects on behavior and neurobiological markers associated with these behavioral changes.

Renal and neurologic effects of cadmium, lead, mercury, and arsenic in children: evidence of early effects and multiple interactions at environmental exposure levels

Lead, cadmium, mercury, and arsenic are common environmental pollutants in industrialized countries, but their combined impact on children's health is little known. We studied their effects on two main targets, the renal and dopaminergic systems, in > 800 children during a cross-sectional European survey. Control and exposed children were recruited from those living around historical nonferrous smelters in France, the Czech Republic, and Poland. Children provided blood and urine samples for the determination of the metals and sensitive renal or neurologic biomarkers. Serum concentrations of creatinine, cystatin C, and beta2-microglobulin were negatively correlated with blood lead levels (PbB), suggesting an early renal hyperfiltration that averaged 7% in the upper quartile of PbB levels (> 55 microg/L; mean, 78.4 microg/L). The urinary excretion of retinol-binding protein, Clara cell protein, and N-acetyl-beta-d-glucosaminidase was associated mainly with cadmium levels in blood or urine and with urinary mercury. All four metals influenced the dopaminergic markers serum prolactin and urinary homovanillic acid, with complex interactions brought to light. Heavy metals polluting the environment can cause subtle effects on children's renal and dopaminergic systems without clear evidence of a threshold, which reinforces the need to control and regulate potential sources of contamination by heavy metals. Key words: arsenic, biomarkers, cadmium, dopaminergic, heavy metals, interactions, lead, mercury, renal.

Effects of arsenite on long-term potentiation in hippocampal slices from young and adult rats

The effects of trivalent arsenite were tested at the Schaffer collateral-CA1 synapse of adult (2-4 month) and young (14-21 days) rats. Exposure of 100micromol/l arsenite led to a slight and reversible reduction of the amplitudes of evoked excitatory postsynaptic field potentials in adult and young rats, while exposure of 0.1 and 1micromol/l arsenite had no effects. The long-term potentiation (LTP) was significantly inhibited by arsenite in adult but not in young rats. Exposure of 0.1, 1 and 100micromol/l arsenite to slices of adult rats before and during the LTP stimulus led to a significant reduction in the potentiated amplitudes amounting to a maximum of 50% of the control values. In young animals, however, exposure of 1micromol/l arsenite showed no effect on the LTP potentiated amplitudes, while exposure of 100micromol/l arsenite led initially to a significant reduction in the amplitudes, compared to the control level, which was completely reversible 20min after washout. Exposure of 100micromol/l arsenite did not affect the paired-pulse facilitation, indicating that arsenite does not exert its effects by influencing presynaptic transmitter release mechanisms.

Blockade and enhancement of glutamate receptor responses in Xenopus oocytes by methylated arsenicals

Pentavalent and trivalent organoarsenic compounds belong to the major metabolites of inorganic arsenicals detected in humans. Recently, the question was raised whether the organic arsenicals represent metabolites of a detoxification process or methylated species with deleterious biological effects. In this study, the effects of trivalent arsenite (AsO(3) (3-); iA(III)), the pentavalent organoarsenic compounds monomethylarsonic acid (CH(3)AsO(OH)(2); MMA(V)) and dimethylarsinic acid ((CH(3))(2)AsO(OH); DMA(V)) and the trivalent compounds monomethylarsonous acid (CH(3)As(OH)(2), MMA(III)) and dimethylarsinous acid ((CH(3))(2)As(OH); DMA(III)) were tested on glutamate receptors and on voltage-operated potassium and sodium channels heterologously expressed in Xenopus oocytes. Membrane currents of ion channels were measured by conventional two-electrode voltage-clamp techniques. The effects of arsenite were tested in concentrations of 1-1,000 micromol/l and the organic arsenical compounds were tested in concentrations of 0.1-100 micromol/l. We found no significant effects on voltage-operated ion channels; however, the arsenicals exert different effects on glutamate receptors. While MMA(V) and MMA(III) significantly enhanced ion currents through N-methyl-D: -aspartate (NMDA) receptor ion channels with threshold concentrations <10 micromol/l, DMA(V) and DMA(III) significantly reduced NMDA-receptor mediated responses with threshold concentrations <0.1 micromol/l; iA(III) had no effects on glutamate receptors of the NMDA type. MMA(III) and DMA(V) significantly reduced ion currents through alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-receptor ion channels with threshold concentrations <10 micromol/l (MMA(III)) and <1 micromol/l (DMA(V)). MMA(V) and iA(III) had no significant effects on glutamate receptors of the AMPA type. The effects of MMA(V), MMA(III), DMA(V) and DMA(III )on glutamate receptors point to a neurotoxic potential of these substances.

A potential mechanism for the impairment of nitric oxide formation caused by prolonged oral exposure to arsenate in rabbits

We have recently found evidence for impairment of nitric oxide (NO) formation and induction of oxidative stress in residents of an endemic area of chronic arsenic poisoning in Inner Mongolia, China. To investigate the underlying mechanisms responsible for these phenomena, a subchronic animal experiment was conducted using male New Zealand White rabbits. After 18 weeks of continuous exposure of rabbits to 5 mg/l of arsenate in drinking water, a significant decrease in systemic NO production occurred, as shown by significantly reduced plasma NO metabolites levels (76% of control) and a tendency towards decreased serum cGMP levels (81.4% of control). On the other hand, increased oxidative stress, as shown by significantly increased urinary hydrogen peroxide (H(2)O(2)) (120% of control), was observed in arsenate-exposed rabbits. In additional experiments measuring aortic tension, the addition of either the calcium ionophore A23187 or acethylcholine (ACh) induced a transient vasoconstriction of aortic rings prepared from arsenate-exposed rabbits, but not in those prepared from control animals. This calcium-dependent contractility action observed in aorta rings from arsenate-exposed rabbits was markedly attenuated by the superoxide (O2(.-)) scavenging enzyme Cu, Zn-SOD, as well as diphenyleneiodonium (DPI) or N(G)-nitro-L-arginine methyl ester (L-NAME), which are inhibitors for nitric oxide synthase (NOS). However, the cyclooxygenase inhibitor indomethacin or the xanthine oxidase blocker allopurinol had no effect on this vasoconstriction. These results suggest that arsenate-mediated reduction of systemic NO may be associated with the enzymatic uncoupling reaction of NOS with a subsequent enhancement of reactive oxygen species such as O2(.-), an endothelium-derived vasoconstricting factor. Furthermore, hepatic levels of (6R)-5,6,7,8-tetrahydro-L-biopterin (BH(4)), a cofactor for NOS, were markedly reduced in arsenate-exposed rabbits to 62% of control, while no significant change occurred in cardiac L-arginine levels. These results suggest that prolonged exposure of rabbits to oral arsenate may impair the bioavailability of BH(4) in endothelial cells and, as a consequence, disrupt the balance between NO and O2(.-) produced from endothelial NOS, such that enhanced free radicals are produced at the expense of NO.

The environmental toxin arsenite induces tau hyperphosphorylation

Abnormally hyperphosphorylated tau polymers known as paired helical filaments constitute one of the major characteristic lesions that lead to the demise of neurons in Alzheimer's disease. Here, we demonstrate that the environmental toxin arsenite causes a significant increase in the phosphorylation of several amino acid residues (Thr-181, Ser-202, Thr-205, Thr-231, Ser-262, Ser-356, Ser-396, and Ser-404) in tau, which are also hyperphosphorylated under pathological conditions. Complementary phosphopeptide mapping revealed a dramatic increase in the (32)P-labeling of many peptides in tau following arsenite treatment. Although arsenite activates extracellular-signal regulated kinases-1/-2 and stress-activated protein kinases, these enzymes did not contribute to the arsenite-increased phosphorylation, nor did they appear to normally modify tau in vivo. Tau phosphorylation induced by arsenite did not involve glycogen synthase kinase-3 or protein phosphatase-1 or -2, but the activity responsible for tau hyperphosphorylation could be inhibited with the protein kinase inhibitor roscovitine. The effects of arsenite on the phosphorylation of some tau mutations (DeltaKappa280, V337M, and R406W) associated with frontal-temporal dementia with parkinsonism linked to chromosome 17 was analyzed. The unchallenged and arsenite-induced phosphorylation of some mutant proteins, especially R406W, was altered at several phosphorylation sites, indicating that these mutations can significantly affect the structure of tau in vivo. Although the major kinase(s) involved in aberrant tau phosphorylation remains elusive, these results indicate that environmental factors, such as arsenite, may be involved in the cascade leading to deregulation of tau function associated with neurodegeneration.

Effects of sodium arsenite exposure on development and behavior in the rat

Arsenic is an environmental contaminant found in soil, water and air in some zones of the world. It has been widely studied for its effects as a human carcinogenic agent, but few studies have dealt with neurobehavioral effects. In addition, studies of arsenic effects on development have only addressed its effects on embryotoxicity and teratogenicity after a single oral, gavage or intraperitoneal exposure. Among the behavioral alterations reported after intoxication with arsenic are both increased and decreased locomotor activity and learning deficits in a delayed alternation task [Toxicol. Lett. 54 (1990) 345; Bull. Environ. Contam. Toxicol. 50 (1993) 100; Brain Res. Bull. 55 (2001) 301]. To further characterize developmental and behavioral alterations induced by arsenic exposure, Sprague-Dawley rats were exposed to arsenite (36.70 mg arsenic/l in drinking water) from gestation day 15 (GD 15) or postnatal day 1 (PND 1), until approximately 4 months old. The pregnant or lactating dams received either the arsenic solution or regular drinking water and once pups were weaned, they continued receiving the same solution as drinking water. Animals exposed from GD 15 showed increased spontaneous locomotor activity and both exposed groups showed increased number of errors in a delayed alternation task in comparison to the control group. Total arsenic (TA) content in brain was similar for both exposed groups and significantly different from the control group. These results indicate that rats exposed to arsenic during development present deficits in spontaneous locomotor activity and alterations in a spatial learning task.