Co-exposure to manganese and lead and pediatric neurocognition in East Liverpool, Ohio

Synergistic suppression of BDNF via epigenetic mechanism deteriorating learning and memory impairment caused by Mn and Pb co-exposure

Microglia, the resident immune cells of the central nervous system (CNS), play a dual role in neurotoxicity by releasing the NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome and brain-derived neurotrophic factor (BDNF) in response to environmental stress. Suppression of BDNF is implicated in learning and memory impairment induced by exposure to manganese (Mn) or lead (Pb) individually. Methyl CpG Binding Protein 2 (MeCp2) and its phosphorylation status are related to BDNF suppression. Protein phosphatase2A (PP2A), a member of the serine/threonine phosphatases family, dephosphorylates substrates based on the methylation state of its catalytic C subunit (PP2Ac). However, the specific impairment patterns and molecular mechanisms resulting from co-exposure to Mn and Pb remain unclear. Therefore, the purpose of this study was to explore the effects of Mn and Pb exposure, alone and in combination, on inducing neurotoxicity in the hippocampus of mice and BV2 cells, and to determine whether simultaneous exposure to both metals exacerbate their toxicity. Our findings reveal that co-exposure to Mn and Pb leads to severe learning and memory impairment in mice, which correlates with the accumulation of metals in the hippocampus and synergistic suppression of BDNF. This suppression is accompanied by up-regulation of the epigenetic repressor MeCp2 and its phosphorylation status, as well as demethylation of PP2Ac. Furthermore, inhibition of PP2Ac demethylation using ABL127, an inhibitor for its protein phosphatase methylesterase1 (PME1), or knockdown of MeCp2 via siRNA transfection in vitro effectively increases BDNF expression and mitigates BV2 cell damage induced by Mn and Pb co-exposure. We also observe abnormal activation of microglia characterized by enhanced release of the NLRP3 inflammasome, Casepase-1 and pro-inflammatory cytokines IL-1β, in the hippocampus of mice and BV2 cells. In summary, our experiments demonstrate that simultaneous exposure to Mn and Pb results in more severe hippocampus-dependent learning and memory impairment, which is attributed to epigenetic suppression of BDNF mediated by PP2A regulation.

Methylphenidate alleviates cognitive dysfunction caused by early manganese exposure: Role of catecholaminergic receptors

Environmental manganese (Mn) exposure is associated with impaired attention and psychomotor functioning, as well as impulsivity/hyperactivity in children and adolescents. We have shown previously that developmental Mn exposure can cause these same dysfunctions in a rat model. Methylphenidate (MPH) lessens impairments in attention, impulse control, and psychomotor function in children, but it is unknown whether MPH ameliorates these dysfunctions when induced by developmental Mn exposure. Here, we sought to (1) determine whether oral MPH treatment ameliorates the lasting attention and sensorimotor impairments caused by developmental Mn exposure, and (2) elucidate the mechanism(s) of Mn neurotoxicity and MPH effectiveness. Rats were given 50 mg Mn/kg/d orally over PND 1-21 and assessed as adults in a series of attention, impulse control and sensorimotor tasks during oral MPH treatment (0, 0.5, 1.5, or 3.0 mg/kg/d). Subsequently, selective catecholaminergic receptor antagonists were administered to gain insight into the mechanism(s) of action of Mn and MPH. Developmental Mn exposure caused persistent attention and sensorimotor impairments. MPH treatment at 0.5 mg/kg/d completely ameliorated the Mn attentional dysfunction, whereas the sensorimotor deficits were ameliorated by the 3.0 mg/kg/d MPH dose. Notably, the MPH benefit on attention was only apparent after prolonged treatment, while MPH efficacy for the sensorimotor deficits emerged early in treatment. Selectively antagonizing D1, D2, or α2A receptors had no effect on the Mn-induced attentional dysfunction or MPH efficacy in this domain. However, antagonism of D2R attenuated the Mn sensorimotor deficits, whereas the efficacy of MPH to ameliorate those deficits was diminished by D1R antagonism. These findings demonstrate that MPH is effective in alleviating the lasting attentional and sensorimotor dysfunction caused by developmental Mn exposure, and they clarify the mechanisms underlying developmental Mn neurotoxicity and MPH efficacy. Given that the cause of attention and psychomotor deficits in children is often unknown, these findings have implications for the treatment of environmentally induced attentional and psychomotor dysfunction in children more broadly.

Independent and Combined Associations of Blood Manganese, Cadmium and Lead Exposures with the Systemic Immune-Inflammation Index in Adults

Manganese (Mn), cadmium (Cd) and lead (Pb) have toxic effects on the immune system. However, their independent and combined effects on immune-inflammation responses are unclear. In recent years, the systemic immune-inflammation index (SII) has been developed as an integrated and novel inflammatory indicator. A retrospective cross-sectional study of 2174 adults ≥20 years old from the National Health and Nutrition Examination Survey (NHANES) 2015-2016 was conducted. Generalized linear models were used to evaluate the independent and combined associations of SII with blood Mn, Cd and Pb levels. As continuous variables, both blood Cd and Mn showed dose-dependent relationships with the SII before and after adjusting for all potential confounding factors. Metal concentrations were then converted into categorical variables. Compared with the adults in the lowest Cd or Mn tertile, those in the highest tertile had higher risks of elevated SII. Furthermore, co-exposure to Mn and Cd also showed a positive relationship with the SII after adjusting for all confounding factors. However, the single effect of Pb exposure and the joint effect of Pb and other metal exposures on the SII were not observed. This study provides important epidemiological evidence of the associations of SII with single and co-exposure effects of blood Mn, Cd, and Pb.

Comparative susceptibility of children and adults to neurological effects of inhaled manganese: A review of the published literature

BACKGROUND

Manganese (Mn) is neurotoxic in adults and children. Current assessments are based on the more extensive adult epidemiological data, but the potential for greater childhood susceptibility remains a concern. To better understand potential lifestage-based variations, we compared susceptibilities to neurotoxicity in children and adults using Mn biomarker data.

METHODS

We developed a literature search strategy based on a Population, Exposures, Comparators, and Outcomes statement focusing on inhalation exposures and neurological outcomes in humans. Screening was performed using DistillerSR. Hair biomarker studies were selected for evaluation because studies with air measurements were unavailable or considered inadequate for children. Studies were paired based on concordant Mn source, biomarker, and outcome. Comparisons were made based on reported dose-response slopes (children vs. adults). Study evaluation was conducted to understand the confidence in our comparisons.

RESULTS

We identified five studies evaluating seven pairings of hair Mn and neurological outcomes (cognition and motor effects) in children and adults matched on sources of environmental Mn inhalation exposure. Two Brazilian studies of children and one of adults reported intelligent quotient (IQ) effects; effects in both comparisons were stronger in children (1.21 to 2.03-fold difference). In paired analyses of children and adults from the United States, children exhibited both stronger and weaker effects compared to adults (0.37 to 1.75-fold differences) on postural sway metrics.

CONCLUSION

There is limited information on the comparative susceptibility of children and adults to inhaled Mn. We report that children may be 0.37 to 2.03 times as susceptible as adults to neurotoxic effects of Mn, thereby providing a quantitative estimate for some aspects of lifestage variation. Due to the limited number of paired studies available in the literature, this quantitative estimate should be interpreted with caution. Our analyses do not account for other sources of inter-individual variation. Additional studies of Mn-exposed children with direct air concentration measurements would improve the evidence base.

Quantitative fluoride imaging of teeth using CaF emission by laser induced breakdown spectroscopy

In this work, we propose the use of molecular emission of calcium fluoride (CaF) by laser induced breakdown spectroscopy (LIBS) to obtain quantitative fluoride distribution images of teeth. LIBS has proved to be an efficient technique to detect low amounts of fluoride in solids, and human teeth have the advantage being a matrix rich in calcium. We used new calibration material from sintered hydroxyapatite pellets doped with fluoride to determine the optimized LIBS conditions of argon flow at 1 L min-1 and using the green emission bands of CaF in 530 nm, and obtained a calibration curve between 0 and 400 μg g-1, and LOD of 18 μg g-1. This methodology was applied within a rat model of fluoride exposure and showed increasing tooth-fluoride with increased exposure dose. To demonstrate applicability of this method in human teeth, we quantified fluoride distribution in teeth from three children from non-fluorinated and fluorinated water regions. Samples from children living in fluoridated water regions showed higher fluoride concentrations in dentine formed after birth, compared to a child from a non-fluoridated region. Teeth have been used as biomarkers for environmental exposure and this new method opens the opportunity in epidemiology research to study critical windows of early life exposure to fluoride as well.

Animal Models of Childhood Exposure to Lead or Manganese: Evidence for Impaired Attention, Impulse Control, and Affect Regulation and Assessment of Potential Therapies

Behavioral disorders involving attention and impulse control dysfunction, such as ADHD, are among the most prevalent disorders in children and adolescents, with significant impact on their lives. The etiology of these disorders is not well understood, but is recognized to be multifactorial, with studies reporting associations with polygenic and environmental risk factors, including toxicant exposure. Environmental epidemiological studies, while good at establishing associations with a variety of environmental and genetic risk factors, cannot establish causality. Animal models of behavioral disorders, when properly designed, can play an essential role in establishing causal relationships between environmental risk factors and a disorder, as well as provide model systems for elucidating underlying neural mechanisms and testing therapies. Here, we review how animal model studies of developmental lead or manganese exposure have been pivotal in (1) establishing a causal relationship between developmental exposure and lasting dysfunction in the domains of attention, impulse control, and affect regulation, and (2) testing the efficacy of specific therapeutic approaches for alleviating the lasting deficits. The lead and manganese case studies illustrate how animal models can advance knowledge in ways that are not possible in human studies. For example, in contrast to the Treatment of Lead Poisoned Children (TLC) human clinical trial evaluating succimer chelation efficacy to improve cognitive functioning in lead-exposed children, our developmental lead exposure animal model showed that succimer chelation can produce lasting cognitive benefits if chelation sufficiently reduces brain lead levels. In addition, this study revealed that succimer treatment in the absence of lead exposure produces lasting cognitive dysfunction, highlighting potential risks of chelation in off-label uses, such as the treatment of autistic children without a history of lead exposure. Our animal model of developmental manganese exposure has demonstrated that manganese can cause lasting attentional and sensorimotor deficits, akin to an ADHD-inattentive behavioral phenotype, thereby providing insights into the role of environmental exposures as contributors to ADHD. These studies have also shown that oral methylphenidate (Ritalin) can fully alleviate the deficits produced by early developmental Mn exposure. Future work should continue to focus on the development and use of animal models that appropriately recapitulate the complex behavioral phenotypes of behavioral disorders, in order to determine the mechanistic basis for the behavioral deficits caused by developmental exposure to environmental toxicants, and the efficacy of existing and emerging therapies.

Environmental Risk Factors and Cognitive Outcomes in Psychosis: Pre-, Perinatal, and Early Life Adversity

Risk for psychosis begins to accumulate as early as the fetal period through exposure to obstetric complications like fetal hypoxia, maternal stress, and prenatal infection. Stressors in the postnatal period, such as childhood trauma, peer victimization, and neighborhood-level adversity, further increase susceptibility for psychosis. Cognitive difficulties are among the first symptoms to emerge in individuals who go on to develop a psychotic disorder. We review the relationship between pre-, perinatal, and early childhood adversities and cognitive outcomes in individuals with psychosis. Current evidence shows that the aforementioned environmental risk factors may be linked to lower overall intelligence and executive dysfunction, beginning in the premorbid period and persisting into adulthood in individuals with psychosis. It is likely that early life stress contributes to cognitive difficulties in psychosis through dysregulation of the body's response to stress, causing changes such as increased cortisol levels and chronic immune activation, which can negatively impact neurodevelopment. Intersectional aspects of identity (e.g., sex/gender, race/ethnicity), as well as gene-environment interactions, likely inform the developmental cascade to cognitive difficulties throughout the course of psychotic disorders and are reviewed below. Prospective studies of birth cohorts will serve to further clarify the relationship between early-life environmental risk factors and cognitive outcomes in the developmental course of psychotic disorders. Specific methodological recommendations are provided for future research.

Gender differences in trace element exposures with cognitive abilities of school-aged children: a cohort study in Wujiang city, China

Trace elements persist in the environment, and their early exposure may adversely affect children's intellectual development. To clarify the influence of blood trace element levels in newborns and school-aged children, we used Wechsler Intelligence Scale for children (WISC-CR) to explore intellectual development level of 148 school-aged children based on a population cohort study. Lead (Pb), selenium (Se), arsenic (As), copper (Cu), manganese (Mn) and chromium (Cr) in cord blood and Pb, As, Cu in venous blood were determined by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometer (AAS). Our analysis of the correlation between children's mental development and trace element content found children's cognitive abilities negatively correlate with Pb (PIQ: β=-0.109, P=0.03737) and Cu (PIQ: β=-0.031, P=0.04431; FISQ: β=-0.031, P=0.02137) levels in cord blood. Prenatal low-level As exposure may negatively affect girls' performance intelligence quotient (PIQ) and verbal intelligence quotient (VIQ). There were differences in Se levels in cord blood and venous blood between boys and girls (P=0.010; P=0.073). High Se levels were associated with a lower VIQ in boys and a higher VIQ in girls. Prenatal exposure to Pb, As and Cu may weaken children's cognitive abilities at school age. Se exposure may have opposite effects on cognitive abilities affected by dose and gender.

Role of p53 methylation in manganese-induced cyclooxygenase-2 expression in BV2 microglial cells

Manganese (Mn) is an essential cofactor for many enzymes and plays an important role in normal growth and development. However, excess exposure to manganese (Mn) may be an important environmental factor leading to neurodegeneration. The overexpression of microglial cyclooxygenase-2 (COX-2) plays a key role in neuroinflammation in neurodegenerative diseases. The existing data suggest that Mn can induce neuroinflammation by up-regulating COX-2 expression. However, the mechanisms involved in Mn-induced microglial COX-2 up-regulation remain to be determined. The aim of this study was to investigate the role of p53 in Mn-induced COX-2 expression in microglial cells. The results showed that Mn exposure induced the up-regulation of COX-2 and inhibited the expression of p53 in BV2 microglial cells. The addition of p53 activator and the over-expression of p53 blocked the expression of COX-2 and prostaglandin E2 (PGE2), a COX-2 downstream effector, induced by Mn. Further, Mn increased the methylation of p53 DNA in microglia, while the addition of demethylation reagent 5-Aza-dC enhanced the expression of p53 but decreased the expression of COX-2. These results suggested that Mn may inhibit p53 expression through induction of DNA methylation, which can further induce the expression of COX-2 in microglial cells.

Probabilistic health risk assessment for residents exposed to potentially toxic elements near typical mining areas in China

Public health problems caused by toxic elements in mining areas have always been an important topic worldwide. However, existing studies have focused on single exposure routes and common toxic elements, which might underestimate the risks faced by residents. In this study, three typical mining areas in central China were selected to assess the health risks of 14 potentially toxic elements through five exposure routes using Monte Carlo simulations. The results indicated that the 95th percentile non-carcinogenic risk values to humans via rice and vegetable ingestion ranged from 9.8 to 26.0 and 6.2 to 19.0. The corresponding carcinogenic risks ranged from 1.4E-2 to 6.3E-2 and from 2.9E-3 to 2.3E-2, respectively. Therefore, residents face serious health risks. Multi-element analysis showed that cadmium (Cd), boron (B), and arsenic (As) were the main contributors to rice non-carcinogenicity, whereas Cd and nickel (Ni) were the main elements of rice carcinogenicity. B and lead (Pb) played an essential role in the non-carcinogenesis of vegetables, and B, Ni, and Cd played an essential role in carcinogenesis. Accidental ingestion is the main route of soil exposure. In these three areas, the probability of non-carcinogenic risk faced by adults was 40%, 0%, and 1%, respectively, while the probabilities for children were 100%, 62%, and 83%, respectively. Regarding carcinogenicity, the risk for both adults and children was up to 100%. This study emphasizes the overall health risks in polluted areas via multi-route and multi-element analysis. This conclusion is helpful to comprehensively assess the potential health risks faced by residents in mining areas and provide baseline data support and a scientific basis for formulating reasonable risk control measures.

Validation of an Analytical Method for the Determination of Manganese and Lead in Human Hair and Nails Using Graphite Furnace Atomic Absorption Spectrometry

This article describes the validation of analytical methods for the determination of Manganese (Mn) and lead (Pb) by graphite furnace atomic absorption spectrometry (GFAAS) in human hair and nail samples. Method validation parameters such as linearity, repeatability, reproducibility, and precision were determined. In addition, the limit of detection (LOD), the limit of quantification (LOQ), and measurement uncertainty were calculated. The developed method was linear in the concentration ranges of 0.001–0.015 and 0.002–0.020 µg·L−1 of Mn and Pb, respectively. The determination coefficients obtained were greater than 0.995. The recoveries obtained after the addition of the standard concentration for the metals ranged from 84.80–107.98%, with a precision not exceeding 12.97% relative standard deviation. The calculated LOD and LOQ for Mn and Pb are within the ranges established by Commission Regulation (EU) No. 836/2011. The expanded uncertainty was estimated to be less than 9.93–6.59% for Mn and Pb. Matrix effects were also studied, finding a smooth effect in both matrices. The analysis of 30 samples of each type revealed the presence of Mn in 30 and Pb in 13 samples. Overall, the proposed validation method was considered optimal for the determination of Mn and Pb.