Estimating the causal effect of prenatal lead exposure on prepulse inhibition deficits in children and adolescents

Exploring the link between the pediatric exposome, respiratory health, and executive function in children: a narrative review

Asthma is a highly prevalent inflammatory condition, significantly affecting nearly six million U.S. children and impacting various facets of their developmental trajectories including neurodevelopment. Evidence supports a link between pediatric environmental exposures in two key areas: asthma and executive function (E.F.). E.F.s are a collective of higher-order cognitive processes facilitating goal-oriented behaviors. Studies also identify asthma-associated E.F. impairments in children. However, limited research has evaluated the inter-relationships among environmental exposures, asthma, and E.F. in children. This review explored relevant research to identify and connect the potential mechanisms and pathways underlying these dynamic associations. The review suggests that the role of the pediatric exposome may function through (1) several underlying biological pathways (i.e., the lung-brain axis, neuroendocrine system, and hypoxia), which could drive asthma and maladaptive E.F. in children and (2) the relationships between the exposome, asthma, and E.F. is a bidirectional linkage. The review reveals essential synergistic links between asthma and E.F. deficits, highlighting the potential role of the pediatric exposome.

A Multigenerational Model of Environmental Risk for Black, Indigenous, and People of Color (BIPOC) Children and Families

BACKGROUND

In recent years, public discourse has increasingly brought institutional and structural racism to the foreground of discussion on the well-being of BIPOC (Black, Indigenous, and People of Color) communities. Environmental toxicity in combination with the social triggers of institutional and structural racism are among the factors that shape the short- and long-term health of BIPOC Americans across multiple lifespans.

OBJECTIVES

We outline a 2 + Generation Model for examining the mechanisms through which institutional and structural racism promotes the intergenerational transmission of environmental health risk and family and interpersonal relationships across the life course and across multiple generations. We present the model's theoretical underpinnings and rationale, discuss model limitations and needed sources of data, and implications for research, policy, and intervention.

DISCUSSION

Parents and children are not only biologically linked in terms of transmission of environmental toxicities, but they are also linked socially and intergenerationally. The 2 + Generation Model foregrounds family and interpersonal relationships occurring within developmental contexts that are influenced by environmental toxicity as well as institutional and structural racism. In sum, the 2 + Generation Model highlights the need for an equity-first interdisciplinary approach to environmental health and redirects the burden of risk reduction away from the individual and onto the institutions and structures that perpetuate the racial disparities in exposure. Doing so requires institutional investment in expanded, multigenerational, and multimethod datasets. https://doi.org/10.1289/EHP13110.

Pilot Monitoring of Lead in Umbilical Cord Blood of Newborns Associated With the Use of Glazed Ceramics from Guanajuato, Mexico

The use of lead-glazed pottery for cooking and storing food, a widespread practice in Mexico, represents a risk of exposure to lead from the human intrauterine stage. Therefore, a pilot study was carried out by means of the measurement of lead in umbilical cord blood by inductively coupled plasma mass spectrometry (ICP-MS) including 69 newborns from the Mexican state capital of Guanajuato, Guanajuato City, where the use of glazed clay is still widespread. Lifestyle and sociodemographic data were collected by interviewing the participating mothers. Hematological parameters and the anthropometry of the newborns and their mothers were analyzed; likewise, the G177C polymorphism in the ALAD gene was genotyped by PCR-RFLP as a marker of genetic vulnerability to lead. The geometric mean of lead in umbilical cord blood was 0.7 µg/dL (< limit of detection = 0.01-28.22). Boys presented higher values than girls (p = 0.03). Only 5.8% of these were above the safety value of the US Centers for Disease Control and Prevention (CDC) of 3.5 µg/dL. Correlations among lead concentrations, maternal age, weeks of gestation, newborn anthropometry, and hematological parameters were not found; however, the participating mothers who reported using glazed ceramics for cooking or storing food had the highest cord-blood lead concentrations (p = 0.04). Regarding genotyping, 97% had ALAD 1, while 3% had ALAD 1, 2; unfortunately, the sample size did not allow analysis of genetic vulnerability to lead. The preparation and conservation of food in handcrafted clay pottery increased the risk of having cord-blood lead values higher than those recommended by the CDC of 3.5 µg/dL (OR = 5; 95% CI:1.3-23; p = 0.01). Our preliminary results suggest that there continues to be intrauterine exposure to lead in Guanajuato.

Prenatal blood lead levels and Birth Weight: a Meta-analysis study

Purpose

Lead, a known toxic metal, causes several adverse reproductive effects, including low birth weight. Fortunately, the exposure level has sharply decreased during the recent decades, but a definitive safe level did not introduce for pregnant women yet. The current meta-analysis study aimed to conduct a quantitative estimation of maternal and umbilical cord blood lead effects on birth weight.

Methods

Two researchers have independently searched the scientific literature for retrieving related studies using the PRISMA criteria for data extraction. Twenty-one full-text articles were selected from primary 5006 titles, limited by the English language and published between 1991 and 2020 on humans.

Results

The pooled mean of maternal and umbilical cord blood lead levels were 6.85 µg/dL (95% CI: 3.36-10.34) and 5.41 µg/dL (95%CI: 3.43-7.40), respectively. The correlation coefficient analysis showed a significant inverse association between the mean maternal blood lead level and birth weight, which was confirmed by Fisher Z-Transformation analysis (-0.374, 95% CI: -0.382, -0.365, p < 0.01). In addition, a significantly lower birth weight (∆: 229 gr, p < 0.05) was found in the relatively high level of maternal blood lead than in low-level exposure (> 5 µg/dL vs. ≤ 5 µg/dL, respectively).

Conclusion

In short, the present study findings suggest an increasing maternal blood lead levels could be a potential risk factor for reducing birth weight. Thus, pregnant women should avoid lead exposure, as much as possible.

Supplementary information

The online version contains supplementary material available at 10.1007/s40201-022-00843-w.

Estimating Causal Effects of Interventions on Early-life Environmental Exposures Using Observational Data

PURPOSE OF REVIEW

We discuss how epidemiologic studies have used observational data to estimate the effects of potential interventions on early-life environmental exposures. We summarize the value of posing questions about interventions, how a group of techniques known as "g-methods" can provide advantages for estimating intervention effects, and how investigators have grappled with the strong assumptions required for causal inference.

RECENT FINDINGS

We identified nine studies that estimated health effects of hypothetical interventions on early-life environmental exposures. Of these, six examined air pollution. Interventions evaluated by these studies included setting exposure levels at a specific value, shifting exposure distributions, and limiting exposure levels to less than a threshold value. Only one study linked exposure contrasts to a specific intervention on an exposure source, however. There is growing interest in estimating intervention effects of early-life environmental exposures, in part because intervention effects are directly related to possible public health actions. Future studies can build on existing work by linking research questions to specific hypothetical interventions that could reduce exposure levels. We discuss how framing questions around interventions can help overcome some of the barriers to causal inference and how advances related to machine learning may strengthen studies by sidestepping the overly restrictive assumptions of parametric regression models. By leveraging advancements in causal inference and exposure science, an intervention framework for environmental epidemiology can guide actionable solutions to improve children's environmental health.

Evaluating the Modulation of the Acoustic Startle Reflex in Children and Adolescents via Vertical EOG and EEG: Sex, Age, and Behavioral Effects

Acoustic startle reflex (ASR) constitutes a reliable, cross-species indicator of sensorimotor and inhibitory mechanisms, showing distinct signature in cognitive aging, sex, and psychopathological characterization. ASR can be modulated by the prepulse inhibition (PPI) paradigm, which comprises the suppression of reactivity to a startling stimulus (pulse) following a weak prepulse (30- to 500-ms time difference), being widely linked to inhibitory capabilities of the sensorimotor system. If the prepulse–pulse tones are more clearly separated (500–2,000 ms), ASR amplitude is enhanced, termed as prepulse facilitation (PPF), reflecting sustained or selective attention. Our study aimed to investigate early-life sensorimotor sex/age differences using Electroencephalographic recordings to measure muscular and neural ASR in a healthy young population. Sixty-three children and adolescents aged 6.2–16.7 years (31 females) took part in the experiment. Neural ASR was assessed by two different analyses, namely, event-related potentials (ERPs) and first-derivative potentials (FDPs). As expected, PPF showed enhanced responses compared with PPI, as indicated by eyeblink, ERP and FDP measures, confirming the gating effect hypothesis. Sex-related differences were reflected in FDPs, with females showing higher ASR than males, suggesting increased levels of poststartle excitability. Intragroup age effects were evaluated via multipredictor regression models, noticing positive correlation between age versus eyeblink and ERP responses. Attention-related ERPs (N100 and P200) showed distinct patterns in PPI versus PPF, potentially indicative for alternative attentional allocation and block-out of sensory overload. Screening measures of participants’ neurodevelopmental (assessed by Wechsler Intelligence Scale for Children) and behavioral (assessed by Child Behavior Checklist) markers were also associated with increased N100/P200 responses, presumably indexing synergy between perceptual consistency, personality profiling, and inhibitory performance. Conclusively, modulation of ASR by PPI and PPF is associated with biological sex and internal/external personality traits in childhood and adolescence, potentially useful to guide symptomatology and prevention of psychopathology.

Prenatal exposure to phthalates and its effects upon cognitive and motor functions: A systematic review

Phthalates are chemicals widely used in packaging and consumer products, which have been shown to interfere with normal hormonal function and development in some human and animal studies. In recent decades, pregnant women's exposure to phthalates has been shown to alter the cognitive outcomes of their babies, and some studies have found delays in motor development.

METHODS

electronic databases including PubMed/MEDLINE and Scopus were searched from their inception to March 2021, using the keywords "phthalate", "cognitive" and "motor".

RESULTS

most studies find statistically significant inverse relationships between maternal urinary phthalate concentration during pregnancy and subsequent outcomes in children's cognitive and motor scales, especially in boys rather than girls. However, many associations are not significant, and there were even positive associations, especially in the third trimester.

CONCLUSION

the relationship between exposure to phthalates during pregnancy and low results on neurocognitive scales is sufficiently clear to adopt policies to reduce exposure. Further studies are needed to analyze sex differences, coordination and motor scales, and phthalate levels during breastfeeding.

Early-life lead exposure and neurodevelopmental disorders

Lead (Pb²⁺) exposure is a global public health problem of major proportion with an alarming number of children with blood Pb²⁺ levels > 10 >g/dL, twice the current CDC reference level for Pb²⁺ exposure. Mounting evidence from population-based studies suggests an association between chronic early life Pb²⁺ exposure (CELLE) and psychiatric disorders, specifically schizophrenia (SZ). Preclinical studies suggest a common mechanism in the pathophysiology of CELLE and SZ, NMDA receptor hypofunction. Here we describe human and experimental animal studies providing the evidence for such an association. Further, recent preclinical studies indicate that Pb²⁺-induced changes in neurotransmitter receptors that mediate the action(s) of drugs of abuse are increased in brain regions associated with addiction circuits in adolescence, a period of increased susceptibility to drug use and abuse and expression of psychiatric disease in humans. In summary, the relationship between the global burden of childhood Pb²⁺ exposure and the latent onset of psychiatric disorders and predisposition to drug use requires further investigations in human populations.

Cognitive Impairment Induced by Lead Exposure during Lifespan: Mechanisms of Lead Neurotoxicity

Lead (Pb) is considered a strong environmental toxin with human health repercussions. Due to its widespread use and the number of people potentially exposed to different sources of this heavy metal, Pb intoxication is recognized as a public health problem in many countries. Exposure to Pb can occur through ingestion, inhalation, dermal, and transplacental routes. The magnitude of its effects depends on several toxicity conditions: lead speciation, doses, time, and age of exposure, among others. It has been demonstrated that Pb exposure induces stronger effects during early life. The central nervous system is especially vulnerable to Pb toxicity; Pb exposure is linked to cognitive impairment, executive function alterations, abnormal social behavior, and fine motor control perturbations. This review aims to provide a general view of the cognitive consequences associated with Pb exposure during early life as well as during adulthood. Additionally, it describes the neurotoxic mechanisms associated with cognitive impairment induced by Pb, which include neurochemical, molecular, and morphological changes that jointly could have a synergic effect on the cognitive performance.

Exposure to environmental neurotoxic substances and neurodevelopment in children from Latin America and the Caribbean

Environmental (and occupational) exposure to neurotoxic substances is a worldwide problem that can affect children's neurodevelopment (ND). In Latin American and Caribbean (LAC) countries there are over 300 million children living under the threat of neurodevelopmental delays due to toxic environmental exposure. Large industrial centers, intense mining and agricultural activities, along with changing complex ecosystems constitute a mosaic that drives contamination of air, water and the food chain. Neurotoxic contaminants such as pesticides (organochlorines, organophosphates, carbamates, pyrethroids, neonicotinoids, and manganese fungicides), chemicals of industrial use (phthalates), and metals (Hg, Pb, Al, As, F, Cd, Mo, Mn) are at the center of environmental exposure studies. Exposure to neurotoxic substances singly or in combination with other compounds or socioeconomic stressors (maternal education, socio-economic and nutritional status) intertwined with occupational and para-occupational exposure can affect ND (motor, cognition, behavior) of children. Significant negative effects of pesticides and neurotoxic elements on ND were found in all studied countries, affecting especially the less-privileged children from laboring families. Studies showed that exposures to the neurotoxicants in human milk are secondary to their more lasting effects during prenatal exposure. This review integrates exposure (prenatal and breastfeeding), metabolism, and ND effects of neurotoxicants. It highlights the overwhelming evidence showing that current levels of exposures are hazardous and detrimental to children's ND in LAC countries. The evidence indicates that a reduction in neurotoxicant exposure is essential to protect children's ND. Therefore, it is urgent to adopt policies and actions that prevent and remediate region-specific children's ND issues.

Chronic developmental lead exposure increases μ-opiate receptor levels in the adolescent rat brain

Childhood lead (Pb2+) intoxication is a global public health problem best known for producing deficits in learning and poor school performance. Human and preclinical studies have suggested an association between childhood Pb2+ intoxication and proclivity to substance abuse and delinquent behavior. While environmental factors have been implicated in opioid addiction, less is known about the role of exposure to environmental pollutants on the brain opioid system. Opioid receptors are involved in the biological effects of opioids and other drugs of abuse. In this study, we examine the effect of chronic developmental Pb2+ exposure (1500 ppm in the diet) on μ-opioid receptor (MOR) levels in the rat brain using [3H]-d-Ala2-MePhe4-Gly-ol5 enkephalin ([3H]-DAMGO) quantitative receptor autoradiography at different developmental stages (juvenile, early-adolescent, late adolescent and adult) in male and female rats. Our results indicate that chronic developmental Pb2+ exposure increases the levels of [3H]-DAMGO specific binding to MOR in juvenile and early adolescent Pb2+-exposed male and female rat brain with no changes in late-adolescent (PN50) and minor changes in Pb2+-exposed adult male rats (PN120). Specifically, at PN14, Pb2+-exposed males had an increase in MOR binding in the lateral posthalamic nuclei (LPTN), and Pb2+-exposed females had increased MOR binding in LPTN, medial thalamus, and hypothalamus. At PN28, Pb2+-exposed males had increased MOR levels in the striatum, stria medullaris of the thalamus, LPTN, medial thalamus, and basolateral amygdala, while Pb2+-exposed females showed an increase in nucleus accumbens core, LPTN, and medial thalamus. No changes were detected in any brain region of male and female rats at PN50, and at PN120 there was a decrease in MOR binding of Pb2+-exposed males in the medial thalamus. Our findings demonstrate age and gender specific effects of MOR levels in the rat brain as a result of chronic developmental Pb2+ exposure. These results indicate that the major changes in brain MOR levels were during pre-adolescence and early adolescence, a developmental period in which there is higher engagement in reward and drug-seeking behaviors in humans. In summary, we show that chronic exposure to Pb2+, an ubiquitous and well-known environmental contaminant and neurotoxicant, alters MOR levels in brain regions associated with addiction circuits in the adolescent period, these findings have important implications for opioid drug use and abuse.