Developmental Windows of Susceptibility to Inorganic Arsenic: A Survey of Current Toxicologic and Epidemiologic Data

Novel covalent organic frameworks based electrospun composite nanofiber membranes as pipette-tip strong anion exchange sorbent for determination of inorganic arsenic in rice

Novel covalent organic frameworks (COFs) based PAN@TpBD(NH₂)₂ electrospun composite nanofiber membranes (ECNMs) were fabricated as strong anion exchange sorbent by implementing electrospinning technology. The finished sorbent was characterized, and key parameters of pipette-tip solid phase extraction (PTSPE) procedures were investigated. Inorganic arsenic (iAs) was successfully separated from rice under the optimal precondition conditions, and quantified by hydride generation-atomic fluorescence spectrometry (HG-AFS). This PTSPE-HG-AFS methodology achieved 0.015 μg L^-1 detection limit, 4.67 % relative standard deviation, and 86.48～99.11 % recoveries. In this work, preparation and characterization of this novel COFs-based anion exchange sorbent, PAN@TpBD(NH₂)₂ ECNMs, is described and its suitability for PTSPE applications is demonstrated.

In utero arsenic exposure and early childhood motor development in the New Hampshire Birth Cohort Study

Introduction

High-level prenatal and childhood arsenic (As) exposure characteristic of several regions in Asia (e.g., Bangladesh), may impact motor function. However, the relationship between lower-level arsenic exposure (characteristic of other regions) and motor development is largely unstudied, despite the potential for deficient motor skills in childhood to have adverse long-term consequences. Thus, we sought to investigate the association between prenatal As exposure and motor function among 395 children in the New Hampshire Birth Cohort Study, a rural cohort from northern New England.

Methods

Prenatal exposure was estimated by measuring maternal urine speciated As at 24-28 weeks of gestation using high-performance liquid chromatography (HPLC) inductively coupled plasma mass spectrometry (ICP-MS) and summing inorganic As, monomethylarsonic acid, and dimethylarsinic acid to obtain total urinary As (tAs). Motor function was assessed with the Bruininks-Oseretsky Test of Motor Proficiency, 2nd Edition (BOT-2) at a mean (SD) age of 5.5 (0.4) years.

Results

Children who completed this exam were largely reported as white race (97%), born to married mothers (86%) with a college degree or higher (67%). The median (IQR) gestational urine tAs concentration was 4.0 (5.0) µg/L. Mean (SD) BOT-2 scores were 48.6 (8.4) for overall motor proficiency and 48.2 (9.6) for fine manual control [standard score = 50 (10)], and were 16.3 (5.1) for fine motor integration and 12.5 (4.1) for fine motor precision [standard score = 15 (5)]. We found evidence of a non-linear dose response relationship and used a change-point model to assess the association of tAs with overall motor proficiency and indices of fine motor integration, fine motor precision, and their composite, fine manual control, adjusted for age and sex. In models adjusted for potential confounders, each doubling of urine tAs decreased overall motor proficiency by -3.3 points (95% CI: -6.1, -0.4) for tAs concentrations greater than the change point of 9.5 µg/L and decreased fine motor integration by -4.3 points (95% CI: -8.0, -0.6) for tAs concentrations greater than the change point of 17.0 µg/L.

Discussion

In summary, we found that levels of prenatal As exposure above an empirically-derived threshold (i.e., the change point) were associated with decrements in childhood motor development in a US population.

Cortical Synaptic Reorganization Under Chronic Arsenic Exposure

There is solid epidemiological evidence that arsenic exposure leads to cognitive impairment, while experimental work supports the hypothesis that it also contributes to neurodegeneration. Energy deficit, oxidative stress, demyelination, and defective neurotransmission are demonstrated arsenic effects, but it remains unclear whether synaptic structure is also affected. Employing both a triple-transgenic Alzheimer's disease model and Wistar rats, the cortical microstructure and synapses were analyzed under chronic arsenic exposure. Male animals were studied at 2 and 4 months of age, after exposure to 3 ppm sodium arsenite in drinking water during gestation, lactation, and postnatal development. Through nuclear magnetic resonance, diffusion-weighted images were acquired and anisotropy (integrity; FA) and apparent diffusion coefficient (dispersion degree; ADC) metrics were derived. Postsynaptic density protein and synaptophysin were analyzed by means of immunoblot and immunohistochemistry, while dendritic spine density and morphology of cortical pyramidal neurons were quantified after Golgi staining. A structural reorganization of the cortex was evidenced through high-ADC and low-FA values in the exposed group. Similar changes in synaptic protein levels in the 2 models suggest a decreased synaptic connectivity at 4 months of age. An abnormal dendritic arborization was observed at 4 months of age, after increased spine density at 2 months. These findings demonstrate alterations of cortical synaptic connectivity and microstructure associated to arsenic exposure appearing in young rodents and adults, and these subtle and non-adaptive plastic changes in dendritic spines and in synaptic markers may further progress to the degeneration observed at older ages.

Metabolism and disposition of arsenic species from controlled dosing with sodium arsenite in adult and neonatal rhesus monkeys. VI. Toxicokinetic studies following oral administration

Arsenic is a common toxic contaminant in food and drinking water. Metabolic activation of arsenic species produces reactive trivalent intermediates that can disrupt cellular regulatory systems by covalent binding to thiol groups. Arsenic exposures have been associated with human diseases including cancer, diabetes, lung and cardiovascular disorders and there is accumulating evidence that early life exposures are important in the etiology. Previous toxicokinetic studies of arsenite ingestion in neonatal CD-1 mice showed consistent evidence for metabolic and physiologic immaturity that led to elevated internal exposures to trivalent arsenic species in the youngest mice, relative to adults. The current study in rhesus monkeys showed that metabolism and binding of trivalent intermediates after arsenite ingestion were similar between adult monkeys and CD-1 mice. Unlike neonatal mice, monkeys from the age of 5-70 days showed similar metabolism and binding profiles, which were also similar to those in adults. The absence of evidence for metabolic immaturity in monkeys suggests that toxicological effects observed in mice from early postnatal exposures to arsenic could over-predict those possible in primates, based on significantly higher internal exposures.

Arsenic Exposure Contributes to the Bioenergetic Damage in an Alzheimer's Disease Model

Worldwide, every year there is an increase in the number of people exposed to inorganic arsenic (iAs) via drinking water. Human populations present impaired cognitive function as a result of prenatal and childhood iAs exposure, while studies in animal models demonstrate neurobehavioral deficits accompanied by neurotransmitter, protein, and enzyme alterations. Similar impairments have been observed in close association with Alzheimer's disease (AD). In order to determine whether iAs promotes the pathophysiological progress of AD, we used the 3xTgAD mouse model. Mice were exposed to iAs in drinking water from gestation until 6 months (As-3xTgAD group) and compared with control animals without arsenic (3xTgAD group). We investigated the behavior phenotype on a test battery (circadian rhythm, locomotor behavior, Morris water maze, and contextual fear conditioning). Adenosine triphosphate (ATP), reactive oxygen species, lipid peroxidation, and respiration rates of mitochondria were evaluated, antioxidant components were detected by immunoblots, and immunohistochemical studies were performed to reveal AD markers. As-3xTgAD displayed alterations in their circadian rhythm and exhibited longer freezing time and escape latencies compared to the control group. The bioenergetic profile revealed decreased ATP levels accompanied by the decline of complex I, and an oxidant state in the hippocampus. On the other hand, the cortex showed no changes of oxidant stress and complex I; however, the antioxidant response was increased. Higher immunopositivity to amyloid isoforms and to phosphorylated tau was observed in frontal cortex and hippocampus of exposed animals. In conclusion, mitochondrial dysfunction may be one of the triggering factors through which chronic iAs exposure exacerbates brain AD-like pathology.

Metabolism and disposition of arsenic species from oral dosing with sodium arsenite in neonatal CD-1 mice. IV. Toxicokinetics following gavage administration and lactational transfer

Arsenic is a ubiquitous contaminant, with typical human dietary intake below 1 μg/kg bw/d and extreme drinking water exposures up to ∼50 μg/kg bw/d. The formation and binding of trivalent metabolites are central to arsenic toxicity and strong human evidence suggests special concern for early life exposures in the etiology of adult diseases, especially cancer. This study measured the metabolism and disposition of arsenite in neonatal mice to understand the role of maturation in metabolic activation and detoxification of arsenic. Many age-related differences were observed after gavage administration of arsenite, with consistent evidence in blood and tissues for higher exposures to trivalent arsenic species in neonatal mice related to the immaturity of metabolic and/or excretory functions. The evidence for greater tissue binding of arsenic species in young mice is consistent with enhanced susceptibility to toxicity based on metabolic and toxicokinetic differences alone. Lactational transfer from arsenite-dosed dams to suckling mice was minimal, based on no dosing-related changes in the levels of arsenic species in pup blood or milk collected from the dams. Animal models evaluating whole-life exposure to inorganic arsenic must use direct dosing in early neonatal life to predict accurately potential toxicity from early life exposures in children.

Metabolism and disposition of arsenic species after repeated oral dosing with sodium arsenite in drinking water. II. Measurements in pregnant and fetal CD-1 mice

Arsenic is ubiquitous in the earth's crust, and human diseases are linked with exposures that are similar to dietary intake estimates. Metabolic methylation of inorganic arsenic facilitates excretion of pentavalent metabolites and decreases acute toxicity; however, tissue binding of trivalent arsenic intermediates is evidence for concomitant metabolic activation. Pregnant and fetal CD-1 mice comprise a key animal model for arsenic carcinogenesis since adult-only exposures have minimal effects. This study evaluated inorganic arsenic and its metabolites in pentavalent and trivalent states in blood and tissues from maternal and fetal CD-1 mice after repeated administration of arsenite through drinking water. After 8 days of exposure, DMA species were ubiquitous in dams and fetuses. Despite the presence of MMA^III in dams, none was observed in any fetal sample. This difference may be important in assessing fetal susceptibility to arsenic toxicity because MMA production has been linked with human disease. Binding of DMA^III in fetal tissues provided evidence for metabolic activation, although the role for such binding in arsenic toxicity is unclear. This study provides links between administered dose, metabolism, and internal exposures from a key animal model of arsenic toxicity to better understand risks from human exposure to environmental arsenic.

Effects of prenatal exposure to endocrine disruptors and toxic metals on the fetal epigenome

Exposure to environmental contaminants during pregnancy has been linked to adverse outcomes at birth and later in life. The link between prenatal exposures and latent health outcomes suggests that these exposures may result in long-term epigenetic reprogramming. Toxic metals and endocrine disruptors are two major classes of contaminants that are ubiquitously present in the environment and represent threats to human health. In this review, we present evidence that prenatal exposures to these contaminants result in fetal epigenomic changes, including altered global DNA methylation, gene-specific CpG methylation and microRNA expression. Importantly, these changes may have functional cellular consequences, impacting health outcomes later in life. Therefore, these epigenetic changes represent a critical mechanism that warrants further study.

Effects of prenatal exposure to endocrine disruptors and toxic metals on the fetal epigenome

Exposure to environmental contaminants during pregnancy has been linked to adverse outcomes at birth and later in life. The link between prenatal exposures and latent health outcomes suggests that these exposures may result in long-term epigenetic reprogramming. Toxic metals and endocrine disruptors are two major classes of contaminants that are ubiquitously present in the environment and represent threats to human health. In this review, we present evidence that prenatal exposures to these contaminants result in fetal epigenomic changes, including altered global DNA methylation, gene-specific CpG methylation and microRNA expression. Importantly, these changes may have functional cellular consequences, impacting health outcomes later in life. Therefore, these epigenetic changes represent a critical mechanism that warrants further study.