Inorganic Arsenic Exposure and Children’s Neurodevelopment: A Review of the Evidence

Selenium and zinc protect against heavy metal mixture-induced, olfactory bulb and hippocampal damage by augmenting antioxidant capacity and activation of Nrf2-Hmox-1 signaling in male rats

PURPOSE/AIM OF THE STUDY

Heavy metals and metalloids have been implicated in neurodenerative diseases. Present study has evaluated the potential protective effects of Se and Zn on heavy metals and metalloids mixture-induced (Cd, Pb, Hg and As) toxicity in the hippocampus and olfactory bulb in male rats.

MATERIALS AND METHODS

Five groups of Wistar rats were randomly divided in to: controls, toxic metals mixture (TMM) exposed rats (PbCl2, 20 mg·kg-1; CdCl2, 1.61 mg·kg-1; HgCl2, 0.40 mg·kg-1 and NaAsO3, 10 mg·kg-1)), TMM + Zn, TMM + Se and TMM-+Zn + Se groups and were orally treated for 60 days.

RESULTS

We found that in hippocampus and olfactory bulb, TMM generated increased lipid peroxidation and diminished antioxidant capacity. These adverse effects induced by TMM were alleviated by Zn and Se co-treatment; moreover, essential trace elements (Zn and Se) decreased activity of acetylcholinesterase, reduced Cd, Pb, Hg and As bioaccumulation in hippocampus and olfactory bulb and decreased levels of TNF-α in the hippocampus. TMM treated rats had lower levels of Hmox-1 (hippocampus), higher levels of Nrf2 (olfactory bulb and hippocampus) and NF-kB (olfactory bulb). TMM treated rats showed significantly highest time in locating the escape hole. Histopathological examination revealed hypertrophied granule cells in OB of TMM exposed rats.

CONCLUSION

Zn and Se supplementation can reverse quaternary mixture-induced (Cd, Pb, Hg and As) toxicity in hippocampus and OB in male albino rats.

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.

Evaluation of School-Age Children's Intelligence Quotient and Their Chronic Exposure to Trace Elements in Ambient Air

Background Children's exposure to different trace elements in their air, water, and food or even present in paints or toys can affect their intelligence quotient (IQ) score. However, this correlation needs to be analyzed and evaluated in different contexts. This study aimed to investigate the associations between airborne concentrations of lead (Pb), manganese (Mn), cadmium (Cd), chromium (Cr), and arsenic (As) and intellectual function in school-age children in Makkah, Kingdom of Saudi Arabia. Methodology Our cohort study aimed to explore the link between exposure to various trace elements in the surrounding air and the IQ scores of children residing in the vicinity of Makkah. We included 430 children in the study and collected information about demographic and lifestyle factors using a structured questionnaire. We employed a mini volume sampler (MiniVol, AirMetrics, Springfield, OR, USA) to collect 24-hour PM10 samples from five locations in Makkah, representing various residential areas with small-to-medium industrial activities and traffic load. We analyzed the samples for Pb, Mn, Cd, Cr, and As concentrations using inductively coupled plasma-mass spectrometry with Perkin Elmer 7300 (Perkin Elmer, Waltham, MA, USA). The combined impact of heavy metals on continuous outcomes was assessed using the Bayesian kernel machine regression model. Results The mean atmospheric concentrations of Pb, Mn, Cd, Cr, and As in summer were 0.093, 0.006, 0.36, 0.15, and 0.017 µg/m³, respectively, while in winter, they were 0.004, 0.003, 0.12, 0.006, and 0.01 µg/m³, respectively. The findings of our study revealed that children's IQ scores were independently associated with co-exposure to the five metals, namely, Pb, Mn, Cd, Cr, and As. Conclusions This study demonstrates a link between combined exposure to five heavy metals (Pb, Mn, Cd, Cr, and As) and children's IQ scores. Regularly evaluating trace elements in children's biological samples is crucial to comprehend their effects on cognitive growth. To explore the possible future health risks of multimetal exposures and their interaction effects, it is imperative to conduct additional studies that involve repeated biological measurements of metal concentrations.

A framework for assessing the impact of chemical exposures on neurodevelopment in ECHO: Opportunities and challenges

The Environmental influences on Child Health Outcomes (ECHO) Program is a research initiative funded by the National Institutes of Health that capitalizes on existing cohort studies to investigate the impact of early life environmental factors on child health and development from infancy through adolescence. In the initial stage of the program, extant data from 70 existing cohort studies are being uploaded to a database that will be publicly available to researchers. This new database will represent an unprecedented opportunity for researchers to combine data across existing cohorts to address associations between prenatal chemical exposures and child neurodevelopment. Data elements collected by ECHO cohorts were determined via a series of surveys administered by the ECHO Data Analysis Center. The most common chemical classes quantified in multiple cohorts include organophosphate pesticides, polychlorinated biphenyls, polybrominated diphenyl ethers, environmental phenols (including bisphenol A), phthalates, and metals. For each of these chemicals, at least four ECHO cohorts also collected behavioral data during infancy/early childhood using the Child Behavior Checklist. For these chemicals and this neurodevelopmental assessment (as an example), existing data from multiple ECHO cohorts could be pooled to address research questions requiring larger sample sizes than previously available. In addition to summarizing the data that will be available, the article also describes some of the challenges inherent in combining existing data across cohorts, as well as the gaps that could be filled by the additional data collection in the ECHO Program going forward.

Heavy Metal Mixture Exposure and Effects in Developing Nations: An Update

The drive for development and modernization has come at great cost. Various human activities in developed and developing countries, particularly in sub-Saharan Africa (SSA) have given rise to environmental safety concerns. Increased artisanal mining activities, illegal refining, use of leaded petrol, airborne dust, arbitrary discarding and burning of toxic waste, absorption of production industries in inhabited areas, inadequate environmental legislation, and weak implementation of policies, have given rise to the incomparable contamination and pollution associated with heavy metals in recent decades. This review evaluates the public health effects of heavy metals and their mixtures in SSA. This shows the extent and size of the problem posed by exposure to heavy metal mixtures in regard to public health.

Heavy metals (Pb, Cd, As and MeHg) as risk factors for cognitive dysfunction: A general review of metal mixture mechanism in brain

Human exposure to toxic heavy metals is a global challenge. Concurrent exposure of heavy metals, such as lead (Pb), cadmium (Cd), arsenic (As) and methylmercury (MeHg) are particularly important due to their long lasting effects on the brain. The exact toxicological mechanisms invoked by exposure to mixtures of the metals Pb, Cd, As and MeHg are still unclear, however they share many common pathways for causing cognitive dysfunction. The combination of metals may produce additive/synergetic effects due to their common binding affinity with NMDA receptor (Pb, As, MeHg), Na⁺ - K⁺ ATP-ase pump (Cd, MeHg), biological Ca⁺² (Pb, Cd, MeHg), Glu neurotransmitter (Pb, MeHg), which can lead to imbalance between the pro-oxidant elements (ROS) and the antioxidants (reducing elements). In this process, ROS dominates the antioxidants factors such as GPx, GS, GSH, MT-III, Catalase, SOD, BDNF, and CERB, and finally leads to cognitive dysfunction. The present review illustrates an account of the current knowledge about the individual metal induced cognitive dysfunction mechanisms and analyse common Mode of Actions (MOAs) of quaternary metal mixture (Pb, Cd, As, MeHg). This review aims to help advancement in mixture toxicology and development of next generation predictive model (such as PBPK/PD) combining both kinetic and dynamic interactions of metals.

Exposure to Mixtures of Metals and Neurodevelopmental Outcomes: A Multidisciplinary Review Using an Adverse Outcome Pathway Framework

Current risk assessment guidance calls for an individual chemical-by-chemical approach that fails to capture potential interactive effects of exposure to environmental mixtures and genetic variability. We conducted a review of the literature on relationships between prenatal and early life exposure to mixtures of lead (Pb), arsenic (As), cadmium (Cd), and manganese (Mn) with neurodevelopmental outcomes. We then used an adverse outcome pathway (AOP) framework to integrate lines of evidence from multiple disciplines based on evolving guidance developed by the Organization for Economic Cooperation and Development (OECD). Toxicological evidence suggests a greater than additive effect of combined exposures to As-Pb-Cd and to Mn with any other metal, and several epidemiologic studies also suggest synergistic effects from binary combinations of Pb-As, Pb-Cd, and Pb-Mn. The exposure levels reported in these epidemiologic studies largely fall at the high-end (e.g., 95th percentile) of biomonitoring data from the National Health and Nutrition Examination Survey (NHANES), suggesting a small but significant potential for high-end exposures. This review integrates multiple data sources using an AOP framework and provides an initial application of the OECD guidance in the context of potential neurodevelopmental toxicity of several metals, recognizing the evolving nature of regulatory interpretation and acceptance.

Trace elements as paradigms of developmental neurotoxicants: Lead, methylmercury and arsenic

Trace elements have contributed unique insights into developmental neurotoxicity and serve as paradigms for such adverse effects. Many trace elements are retained in the body for long periods and can be easily measured to assess exposure by inexpensive analytical methods that became available several decades ago so that past and cumulated exposures could be easily characterized through analysis of biological samples, e.g. blood and urine. The first compelling evidence resulted from unfortunate poisoning events that allowed scrutiny of long-term outcomes of acute exposures that occurred during early development. Pursuant to this documentation, prospective studies of children's cohorts that applied sensitive neurobehavioral methods supported the notion that the brain is uniquely vulnerable to toxic damage during early development. Lead, methylmercury, and arsenic thereby serve as paradigm neurotoxicants that provide a reference for other substances that may have similar adverse effects. Less evidence is available on manganese, fluoride, and cadmium, but experience from the former trace elements suggest that, with time, adverse effects are likely to be documented at exposures previously thought to be low and safe.