Neurofunctional dopaminergic impairment in elderly after lifetime exposure to manganese

Impact of Manganese on Neuronal Function: An Exploratory MultiOmic Study on Ferroalloy Workers in Brescia, Italy

Interest is growing in the potential role of manganese (Mn) in Alzheimer's Disease (ADRD). This nested pilot study of a ferroalloy workers cohort was aimed to investigate the effects of long-term occupational Mn exposure on cognitive function through β-amyloid (Aβ) modification and brain deposition, as well as metabolomic, lipidomic and proteomic profiling. We examined 6 male exposed workers (median age 63, exposure duration 31 yrs), and 5 historical controls (median age 60) who had undergone brain PET scan imaging showing higher Aβ deposition among the exposed compared to the controls (p < 0.05). The average annual cumulative respirable Mn of the ferroalloy workers was 329.23 ± 516.39 μg/m3 (geometric mean 118.59). Average Mn level in plasma of the exposed subjects (0.704 ± 0.2 ng/mL) was significantly higher than the controls (0.397 ± 0.18). Pathway analyses using LC-MS/MS results revealed impacted metabolomic pathways such as olfactory signaling, mitochondrial fatty acid beta-oxidation, biogenic amine synthesis, SLC-mediated transmembrane transport, and glycerophospholipid and choline metabolism in the Mn exposed group. Single molecule arrays (Simoa) analysis revealed notable modifications of AD-related plasma biomarkers; protein microarray (chip) showed significant changes (p < 0.05) in the levels of some plasma antibodies targeting autoimmune and neuronal associated proteins such as Aβ (25-35), GFAP, Serotonin, Human NOVA1, and Human Siglec-1/CD169 among the Mn exposed individuals. This data provides evidence on Mn-induced alterations of pathways and biomarkers associated with cognitive neurodegenerative diseases.

Impact of manganese and metal mixtures in blood, hair, and soil on child adaptive behaviors in Southeast Side Chicago

BACKGROUND

Manganese (Mn) is essential in growth and development, yet higher levels of Mn are associated with deficits in neurodevelopment. Elevated air Mn was identified near Mn alloy processing facilities in Southeast Side Chicago resulting in community concern about child exposure and health.

METHODS

Blood, hair, and soil samples were collected and analyzed for multiple metals for children ages 7-17 years and a parent/primary caregiver completed surveys. We used generalized estimating equations to assess associations between metals and the Adaptive Behavior Assessment System 3rd Edition (ABAS-3) scores. Sensitivity analyses were conducted to determine effect modification by child sex on associations between metals and ABAS-3 scores. Bayesian kernel machine regression was used as our principal analytic framework to assess the associations between metal mixtures and adaptive behaviors.

RESULTS

The analyses included 108 children. Residential distance from the nearest Mn industrial source was inversely correlated with soil Mn levels and some were above the federal screening level. A significant association was found between soil Mn and lower ABAS-3 score (β: 3.78, 95 % CI: 7.31, -0.25), and between blood Mn and lower scores in females (β: 11.8, 95 % CI: 21.7, -1.87). ABAS-3 scores were negatively associated with the blood metals mixture, primarily driven by Mn.

CONCLUSION

Children in Southeast Side Chicago have elevated levels of soil Mn and soil Mn was associated with poorer ABAS-3 scores. Sex-specific differences were found between metal levels and ABAS-3 scores. After considering multiple metals in mixture, Mn was the primary driver of poorer adaptive behavior.

The Role of Prenatal Exposure to Lead and Manganese in Child Cognitive Neurodevelopment at 18 Months: The Results of the Italian PHIME Cohort

Prenatal lead (Pb) and manganese (Mn) exposure can impair neurodevelopment, targeting the central nervous system. This study investigated the effects of prenatal exposure to Pb and Mn on neurodevelopment in children at 18 months of age, using data from 607 Italian mother-child pairs enrolled in the Northern Adriatic Cohort II (NAC-II). All children born at term (≥37 weeks) were assessed with the Bayley Scales of Infant and Toddler Development, third edition. Cord blood concentrations of Mn and Pb were categorized as low or high exposures based on the 75th percentile of their distribution. Sociodemographic and lifestyle information was collected via questionnaires. Using simple and multiple linear regressions, the study examined the relationship between the cognitive composite score (COGN) and Mn and Pb co-exposure, including their interaction. Stratified regressions explored how Mn exposure influenced the effect of Pb, in the whole cohort and by the child's sex. Beta coefficients (β) and the 90% confidence interval (90% CI) were estimated. Boys showed an interaction effect between Mn and Pb, with a reduction in COGN (β = -5.78, 90% CI: -11.17; -0.40), further described as a negative effect of high Pb on cognition when Mn exposure was also high (β = -6.98, 90% CI: -10.93; -3.04). No clear effects were observed in girls or the entire cohort at these levels of exposure. The findings highlight the harmful impact of combined prenatal Pb and Mn exposure on cognitive development in boys.

Neurological and neurobehavioral effects of welders in Egypt exposed to manganese containing welding fumes

PURPOSE

Welders are more likely to develop neurobehavioral disorders because of their exposure to neurotoxic metals such as manganese. This study aimed to measure the neurobehavioral performance of welders occupationally exposed to manganese at welding enterprises and its relationship with the workplace environment.

METHODS

It is a comparative cross-sectional study carried out on 130 welders working at 50 welding enterprises in Menoufia governorate, Egypt, compared to 130 non-occupationally exposed controls.

RESULTS

It was found that the environments of the studied welding enterprises had levels of respirable dust, manganese, and total welding fumes that exceeded internationally permissible limits. In addition, the mean blood manganese levels were significantly higher among welders (4.16 ± 0.61) than the controls (1.72 ± 0.41). Welders had a significantly higher prevalence of neurological manifestations and lower performance of neurobehavioral tests. Lower neurobehavioral performance among welders was significantly correlated with increased work duration and blood levels in some tests.

CONCLUSION

To lessen the fumes in the breathing zone of workers, it is therefore strongly recommended to regularly wear high-quality personal protective equipment, especially masks, and to ensure proper ventilation.

Sex-specific associations of a ferroalloy metal mixture with motor function in Italian adolescents

Background

Motor function is critical for children's health, yet remains an understudied neurodevelopmental domain. Exposure to metals has been linked with motor function, but no study has examined the joint effects of metal mixtures.

Methods

We evaluated cross-sectional associations between a metal mixture and motor function among 569 adolescents (10-14 years old) living near the ferroalloy industry. Concentrations of blood lead, hair manganese, hair copper, and hair chromium were quantified using inductively coupled plasma mass spectrometry. Neuropsychologists administered multiple fine motor function assessments: pursuit aiming, finger tapping, visual reaction time (VRT), and subtests from the Luria Nebraska battery. We estimated associations between motor function and the metal mixture using quantile-based g-computation and multivariable linear regression, adjusting for child age, sex, and socioeconomic status. We explored sex-specific associations in stratified models.

Results

Associations between the metal mixture and motor function were mostly null but were modified by sex. We observed a beneficial association among females: a quartile increase in all metals in the mixture was associated with a 2.6% faster average response time on the VRT (95% confidence interval [CI] = -4.7%, -0.5%), driven by Cu and Cr. In contrast, this association was adverse among males (ß = 1.5% slower response time [95% CI = -0.7%, 3.9%]), driven by Cu and Mn.

Conclusions

Results suggest that males may be more susceptible to the adverse effects of metal exposure on motor function during adolescence than females. Future studies, particularly prospective study designs, are warranted to further understand the associations of metal mixtures with motor function.

Child and Adolescent Manganese Biomarkers and Adolescent Postural Balance in Marietta CARES Cohort Participants

BACKGROUND

Manganese (Mn) plays a significant role in both human health and global industries. Epidemiological studies of exposed populations demonstrate a dose-dependent association between Mn and neuromotor effects ranging from subclinical effects to a clinically defined syndrome. However, little is known about the relationship between early life Mn biomarkers and adolescent postural balance.

OBJECTIVES

This study investigated the associations between childhood and adolescent Mn biomarkers and adolescent postural balance in participants from the longitudinal Marietta Communities Actively Researching Exposures Study (CARES) cohort.

METHODS

Participants were recruited into CARES when they were 7-9 y old, and reenrolled at 13-18 years of age. At both time points, participants provided samples of blood, hair, and toenails that were analyzed for blood Mn and lead (Pb), serum cotinine, hair Mn, and toenail Mn. In adolescence, participants completed a postural balance assessment. Greater sway indicates postural instability (harmful effect), whereas lesser sway indicates postural stability (beneficial effect). Multivariable linear regression models were conducted to investigate the associations between childhood and adolescent Mn biomarkers and adolescent postural balance adjusted for age, sex, height-weight ratio, parent/caregiver intelligence quotient, socioeconomic status, blood Pb, and serum cotinine.

RESULTS

CARES participants who completed the adolescent postural balance assessment (n = 123 ) were 98% White and 54% female and had a mean age of 16 y (range: 13-18 y). In both childhood and adolescence, higher Mn biomarker concentrations were significantly associated with greater adolescent sway measures. Supplemental analyses revealed sex-specific associations; higher childhood Mn biomarker concentrations were significantly associated with greater sway in females compared with males.

DISCUSSION

This study found childhood and adolescent Mn biomarkers were associated with subclinical neuromotor effects in adolescence. This study demonstrates postural balance as a sensitive measure to assess the association between Mn biomarkers and neuromotor function. https://doi.org/10.1289/EHP13381.

Mixed Metal Components in PM2.5 Contribute to Chemokine Receptor CCR5-Mediated Neuroinflammation and Neuropathological Changes in the Mouse Olfactory Bulb

Particulate matter, especially PM2.5, can invade the central nervous system (CNS) via the olfactory pathway to induce neurotoxicity. The olfactory bulb (OB) is the key component integrating immunoprotection and olfaction processing and is necessarily involved in the relevant CNS health outcomes. Here we show that a microglial chemokine receptor, CCR5, is the target of environmentally relevant PM2.5 in the OB to trigger neuroinflammation and then neuropathological injuries. Mechanistically, PM2.5-induced CCR5 upregulation results in the pro-inflammatory paradigm of microglial activation, which subsequently activates TLR4-NF-κB neuroinflammation signaling and induces neuropathological changes that are closely related to neurodegenerative disorders (e.g., Aβ deposition and disruption of the blood-brain barrier). We specifically highlight that manganese and lead in PM2.5 are the main contributors to CCR5-mediated microglial activation and neuroinflammation in synergy with aluminum. Our results uncover a possible pathway of PM2.5-induced neuroinflammation and identify the principal neurotoxic components, which can provide new insight into efficiently diminishing the adverse health effects of PM2.5.

A partial Drp1 knockout improves autophagy flux independent of mitochondrial function

BACKGROUND

Dynamin-related protein 1 (Drp1) plays a critical role in mitochondrial dynamics. Partial inhibition of this protein is protective in experimental models of neurological disorders such as Parkinson's disease and Alzheimer's disease. The protective mechanism has been attributed primarily to improved mitochondrial function. However, the observations that Drp1 inhibition reduces protein aggregation in such neurological disorders suggest the involvement of autophagy. To investigate this potential novel protective mechanism of Drp1 inhibition, a model with impaired autophagy without mitochondrial involvement is needed.

METHODS

We characterized the effects of manganese (Mn), which causes parkinsonian-like symptoms in humans, on autophagy and mitochondria by performing dose-response studies in two cell culture models (stable autophagy HeLa reporter cells and N27 rat immortalized dopamine neuronal cells). Mitochondrial function was assessed using the Seahorse Flux Analyzer. Autophagy flux was monitored by quantifying the number of autophagosomes and autolysosomes, as well as the levels of other autophagy proteins. To strengthen the in vitro data, multiple mouse models (autophagy reporter mice and mutant Drp1+/- mice and their wild-type littermates) were orally treated with a low chronic Mn regimen that was previously reported to increase α-synuclein aggregation and transmission via exosomes. RNAseq, laser captured microdissection, immunofluorescence, immunoblotting, stereological cell counting, and behavioural studies were used. RESULTS IN VITRO: data demonstrate that at low non-toxic concentrations, Mn impaired autophagy flux but not mitochondrial function and morphology. In the mouse midbrain, RNAseq data further confirmed autophagy pathways were dysregulated but not mitochondrial related genes. Additionally, Mn selectively impaired autophagy in the nigral dopamine neurons but not the nearby nigral GABA neurons. In cells with a partial Drp1-knockdown and Drp1+/- mice, Mn induced autophagic impairment was significantly prevented. Consistent with these observations, Mn increased the levels of proteinase-K resistant α-synuclein and Drp1-knockdown protected against this pathology.

CONCLUSIONS

This study demonstrates that improved autophagy flux is a separate mechanism conferred by Drp1 inhibition independent of its role in mitochondrial fission. Given that impaired autophagy and mitochondrial dysfunction are two prominent features of neurodegenerative diseases, the combined protective mechanisms targeting these two pathways conferred by Drp1 inhibition make this protein an attractive therapeutic target.

Association between the Composition of Drinking Water and Cognitive Function in the Elderly: A Systematic Review

The prevalence of dementia increases with nearly 10 million new cases each year, with Alzheimer's disease contributing to 60-70% of cases. Environmental factors such as drinking water have been evaluated to determine if a relationship exists between trace elements in drinking water and the risk of developing cognitive disorders in the elderly. The purpose of the current systematic review was to evaluate an association between the composition of drinking water and cognitive function in the elderly. In accordance with the Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines, a literature search was conducted using PubMed and CINAHL databases. A total of 10 studies were included in the current systematic review. Aluminum is the most commonly evaluated trace element in studies (n = 8), followed by silica (n = 5), calcium (n = 4), and fluoride (n = 4). Aluminum exposure showed an increased risk of cognitive decline in four studies, with no association reported in the other studies. Higher silica and pH levels were shown to be protective against a decline in cognitive function. A similar protective effect of calcium was found in two studies. Future research should measure multiple trace mineral levels in all water sources to evaluate the impact on cognitive function.

Metal-ion transporter SLC39A8 is required for brain manganese uptake and accumulation

Manganese (Mn) is an essential nutrient, but is toxic in excess. Whole-body Mn levels are regulated in part by the metal-ion influx transporter SLC39A8, which plays an essential role in the liver by reclaiming Mn from bile. Physiological roles of SLC39A8 in Mn homeostasis in other tissues, however, remain largely unknown. To screen for extrahepatic requirements for SLC39A8 in tissue Mn homeostasis, we crossed Slc39a8-inducible global-KO (Slc39a8 iKO) mice with Slc39a14 KO mice, which display markedly elevated blood and tissue Mn levels. Tissues were then analyzed by inductively coupled plasma-mass spectrometry to determine levels of Mn. Although Slc39a14 KO; Slc39a8 iKO mice exhibited systemic hypermanganesemia and increased Mn loading in the bone and kidney due to Slc39a14 deficiency, we show Mn loading was markedly decreased in the brains of these animals, suggesting a role for SLC39A8 in brain Mn accumulation. Levels of other divalent metals in the brain were unaffected, indicating a specific effect of SLC39A8 on Mn. In vivo radiotracer studies using 54Mn in Slc39a8 iKO mice revealed that SLC39A8 is required for Mn uptake by the brain, but not most other tissues. Furthermore, decreased 54Mn uptake in the brains of Slc39a8 iKO mice was associated with efficient inactivation of Slc39a8 in isolated brain microvessels but not in isolated choroid plexus, suggesting SLC39A8 mediates brain Mn uptake via the blood-brain barrier. These findings establish SLC39A8 as a candidate therapeutic target for mitigating Mn uptake and accumulation in the brain, the primary organ of Mn toxicity.

Manganese-Induced Parkinsonism: Evidence from Epidemiological and Experimental Studies

Manganese (Mn) exposure has evolved from acute, high-level exposure causing manganism to low, chronic lifetime exposure. In this latter scenario, the target areas extend beyond the globus pallidus (as seen with manganism) to the entire basal ganglia, including the substantia nigra pars compacta. This change of exposure paradigm has prompted numerous epidemiological investigations of the occurrence of Parkinson's disease (PD), or parkinsonism, due to the long-term impact of Mn. In parallel, experimental research has focused on the underlying pathogenic mechanisms of Mn and its interactions with genetic susceptibility. In this review, we provide evidence from both types of studies, with the aim to link the epidemiological data with the potential mechanistic interpretation.

A partial Drp1 knockout improves autophagy flux independent of mitochondrial function

Dynamin-related protein 1 (Drp1) is typically known for its role in mitochondrial fission. A partial inhibition of this protein has been reported to be protective in experimental models of neurodegenerative diseases. The protective mechanism has been attributed primarily to improved mitochondrial function. Herein, we provide evidence showing that a partial Drp1-knockout improves autophagy flux independent of mitochondria. First, we characterized in cell and animal models that at low non-toxic concentrations, manganese (Mn), which causes parkinsonian-like symptoms in humans, impaired autophagy flux but not mitochondrial function and morphology. Furthermore, nigral dopaminergic neurons were more sensitive than their neighbouring GABAergic counterparts. Second, in cells with a partial Drp1-knockdown and Drp1 +/- mice, autophagy impairment induced by Mn was significantly attenuated. This study demonstrates that autophagy is a more vulnerable target than mitochondria to Mn toxicity. Furthermore, improving autophagy flux is a separate mechanism conferred by Drp1 inhibition independent of mitochondrial fission.

Association of air pollution with olfactory identification performance of São Paulo residents: a cross-sectional study

OBJECTIVE

Exposure to particulate matter of 10 μm or less in diameter (PM₁₀) has been implicated in pulmonary and cardiovascular diseases. However, the effect of PM₁₀ on olfaction has not been well established. We estimated individual acute and chronic PM₁₀ exposure levels in a large Brazilian cohort and related them to the ability to identify odors.

METHODS

Adults from São Paulo (n = 1358) were recruited from areas with different levels of air pollution. To verify individual exposure to air pollution, the averages of 30, 60, 90, 180 and 364 days of PM₁₀ were interpolated to subjects' zip codes using the kriging method. Olfactory identification performance was tested using the University of Pennsylvania Smell Identification Test (UPSIT®). Multiple linear regressions were used to calculate the effect of air pollution on olfactory identification performance, controlling for demographic and other variables that affect the sense of smell.

RESULTS

Acute exposures to PM₁₀ were related to worse UPSIT® scores, including 30- (β =  - 0.94, 95% Confidence Interval [CI]  - 0.98,  - 0.89), 60- (β =  - 1.09, 95% CI = - 1.13,  - 1.04) and 90-day intervals (β =  - 1.06, 95% CI  - 1.10,  - 1.02) (reference for β: 1 µm/m³ increase in PM10 exposure per point decrease in UPSIT® score). Chronic exposures were also associated with worse olfaction for both 180- (β =  - 1.06, 95% CI  - 1.10,  - 1.03) and 364-day (β =  - 0.87, 95% CI  - 0.90,  - 0.84) intervals. As in prior work, men, older, low-income, and low-schooling people demonstrated worse olfactory performance.

CONCLUSION

Acute and chronic exposure to PM₁₀ is strongly associated with olfactory identification performance in Brazilian adults. Understanding the mechanisms which underlie these relationships could help to improve chemosensory function with a large public health impact.

Material properties of degradable alloy Fe-30Mn-0.6N and its effect on ferroptosis in synoviocytes

Ferroalloy has shown potential as implant materials, but little attention has been paid to their effects on synovial tissue ferroptosis. This study aimed to examine the mechanical properties, degradability and biocompatibility of Fe-30Mn-0.6N alloy and effects of it on synovial tissue ferroptosis. Tensile testing showed that Fe-30Mn-0.6N alloys exhibited tensile strength of 487 ± 18 MPa, yield strength of 221 ± 10 MPa, elongation of 16.9 ± 0.3% and Young's modulus of 37.7 ± 1.3 GPa. In vivo experiments, the cross-sectional area of the Fe-30Mn-0.6N alloys decreased by 73.32 ± 12.73% after 8 weeks of implantation. The results of scanning electron microscopy (SEM) and surface elemental analysis (EDS) showed that the Fe-30Mn-0.6N alloys had more Ca, O, C and P element deposition (p < .05). After 2, 4 and 8 weeks of implantation, no inflammatory response was observed in peri-implant synovial tissue of Fe-30Mn-0.6N and Ti-6Al-4V alloys, and Fe-30Mn-0.6N alloys did not affect the expression of the ferroptosis inhibitory gene Glutathione peroxidase 4 (GPX4). Compared with the control group, 30% Fe-30Mn-0.6N alloy extracts did not affect the cell viability (p > .05) in vitro, and intracellular Fe²⁺ and the reactive oxygen species (ROS) was significantly reduced (p < .05). WB and PCR results showed that the 30% extracts increased the protein activity and mRNA expression of GPX4, FTH1 and SLC7A11 in synoviocytes, but had no effect on PTGS2 and p53. It is concluded that Fe-30Mn-0.6N had degradability and biocompatibility in peri-implant synovial tissue, and did not induce significantly ferroptosis in synoviocytes.

Air Pollution: Possible Interaction between the Immune and Nervous System?

Exposure to environmental pollutants is a serious and common public health concern associated with growing morbidity and mortality worldwide, as well as economic burden. In recent years, the toxic effects associated with air pollution have been intensively studied, with a particular focus on the lung and cardiovascular system, mainly associated with particulate matter exposure. However, epidemiological and mechanistic studies suggest that air pollution can also influence skin integrity and may have a significant adverse impact on the immune and nervous system. Air pollution exposure already starts in utero before birth, potentially causing delayed chronic diseases arising later in life. There are, indeed, time windows during the life of individuals who are more susceptible to air pollution exposure, which may result in more severe outcomes. In this review paper, we provide an overview of findings that have established the effects of air pollutants on the immune and nervous system, and speculate on the possible interaction between them, based on mechanistic data.

Neurocognitive function in adult residents of a mining district in Mexico after reducing manganese exposure: Follow-up after 11 years

BACKGROUND

Little is known about the neurotoxic effects of chronic exposure to airborne Mn once exposure has been reduced. The environmentally exposed and the reference adult populations evaluated in 2002 were followed, after an environmental management program (EMP) was implemented to reduce the exposure in a mining district in Mexico.

OBJECTIVE

The aim of this study was to compare the association between exposure to Mn and neurocognitive performance in environmentally exposed and reference groups of adults before and after EMP implementation.

METHODS

In 2013, the same battery of neurocognitive tests used in the initial study (2002) was applied to 58 adults exposed to airborne Mn and 30 adults from the reference community. A cumulative exposure index (CEI) was estimated for the study population before and after the EMP. Categorical outcomes were analyzed using logistic regression, and the resulting ORs were compared between studies. Continuous outcomes were analyzed using linear regression. All models were adjusted for age, years of education, socioeconomic status and blood lead levels.

RESULTS

Exposed adults from the post-EMP study showed an improvement in fine motor and verbal regulation of motor skills (OR < 1) compared to the exposed adults from the pre-EMP study (OR > 1). In both pre- and post-studies, the exposed adults showed a deterioration in their dynamic organization of motor activity compared to the reference group (p < 0.05); however, they showed no significant change in attention and working-memory performance.

DISCUSSION

After four years of a significant reduction in airborne Mn levels resulting from EMP implementation, chronically exposed adults showed an improvement in fine motor and verbal regulation of motor skills; however, the remaining areas of their motor and cognitive functions remained impaired.

The mitochondrial RNA granule modulates manganese-dependent cell toxicity

Prolonged manganese exposure causes manganism, a neurodegenerative movement disorder. The identity of adaptive and nonadaptive cellular processes targeted by manganese remains mostly unexplored. Here we study mechanisms engaged by manganese in genetic cellular models known to increase susceptibility to manganese exposure, the plasma membrane manganese efflux transporter SLC30A10 and the mitochondrial Parkinson's gene PARK2. We found that SLC30A10 and PARK2 mutations as well as manganese exposure compromised the mitochondrial RNA granule composition and function, resulting in disruption of mitochondrial transcript processing. These RNA granule defects led to impaired assembly and function of the mitochondrial respiratory chain. Notably, cells that survived a cytotoxic manganese challenge had impaired RNA granule function, thus suggesting that this granule phenotype was adaptive. CRISPR gene editing of subunits of the mitochondrial RNA granule, FASTKD2 or DHX30, as well as pharmacological inhibition of mitochondrial transcription-translation, were protective rather than deleterious for survival of cells acutely exposed to manganese. Similarly, adult Drosophila mutants with defects in the mitochondrial RNA granule component scully were safeguarded from manganese-induced mortality. We conclude that impairment of the mitochondrial RNA granule function is a protective mechanism for acute manganese toxicity.

Associations of Heavy Metals with Activities of Daily Living Disability: An Epigenome-Wide View of DNA Methylation and Mediation Analysis

BACKGROUND

Exposure to heavy metals has been reported to be associated with multiple diseases. However, direct associations and potential mechanisms of heavy metals with physical disability remain unclear.

OBJECTIVES

We aimed to quantify associations of heavy metals with physical disability and further explore the potential mechanisms of DNA methylation on the genome scale.

METHODS

A cross-sectional study of 4,391 older adults was conducted and activities of daily living (ADL) disability were identified using a 14-item scale questionnaire including basic and instrumental activities to assess the presence of disability (yes or no) rated on a scale of dependence. Odds ratios (ORs) and 95% confidence intervals (CI) were estimated to quantify associations between heavy metals and ADL disability prevalence using multivariate logistic regression and Bayesian kernel machine regression (BKMR) models. Whole blood-derived DNA methylation was measured using the HumanMethylationEPIC BeadChip array. An ADL disability-related epigenome-wide DNA methylation association study (EWAS) was performed among 212 sex-matched ADL disability cases and controls, and mediation analysis was further applied to explore potential mediators of DNA methylation.

RESULTS

Each 1-standard deviation (SD) higher difference in log10-transformed manganese, copper, arsenic, and cadmium level was significantly associated with a 14% (95% CI: 1.05, 1.24), 16% (95% CI:1.07, 1.26), 22% (95% CI:1.13, 1.33), and 15% (95% CI:1.06, 1.26) higher odds of ADL disability, which remained significant in the multiple-metal and BKMR models. A total of 85 differential DNA methylation sites were identified to be associated with ADL disability prevalence, among which methylation level at cg220000984 and cg23012519 (annotated to IRGM and PKP3) mediated 31.0% and 31.2% of manganese-associated ADL disability prevalence, cg06723863 (annotated to ESRP2) mediated 32.4% of copper-associated ADL disability prevalence, cg24433124 (nearest to IER3) mediated 15.8% of arsenic-associated ADL disability prevalence, and cg07905190 and cg17485717 (annotated to FREM1 and TCP11L1) mediated 21.5% and 30.5% of cadmium-associated ADL disability prevalence (all p<0.05).

DISCUSSION

Our findings suggested that heavy metals contributed to higher prevalence of ADL disability and that locus-specific DNA methylation are partial mediators, providing potential biomarkers for further cellular mechanism studies. https://doi.org/10.1289/EHP10602.

Biomarkers of environmental manganese exposure

We conducted a critical review on biomarkers of environmental manganese (Mn) exposure to answer the following questions: 1) are there reliable biomarkers of internal Mn exposure (Mn in biological matrices) associated with external metrics of Mn exposure (Mn in environmental media)? and 2) are there accurate reference values (RVs) for Mn in biological matrices? Three bibliographic databases were searched for relevant references and identified references were screened by two independent reviewers. Of the 6342 unique references identified, 86 articles were retained for data abstraction. Our analysis of currently available evidence suggests that Mn levels in blood and urine are not useful biomarkers of Mn exposure in non-occupational settings. The strength of the association between Mn in environmental media and saliva was variable. Findings regarding the utility of hair Mn as a biomarker of environmental Mn exposure are inconsistent. Measurements of Mn in teeth are technically challenging and findings on Mn in tooth components are scarce. In non-occupationally exposed individuals, bone Mn measurements using in vivo neutron activation analysis (IVNAA) are associated with large uncertainties. Findings suggest that Mn in nails may reflect Mn in environmental media and discriminate between groups of individuals exposed to different environmental Mn levels, although more research is needed. Currently, there is no strong evidence for any biological matrix as a valid biomarker of Mn exposure in non-occupational settings. Because of methodological limitations in studies aimed at derivation of RVs for Mn in biological materials, accurate RVs are scarce.

Poorer cognitive function and environmental airborne Mn exposure determined by biomonitoring and personal environmental monitors in a healthy adult population

BACKGROUND/AIM

In the Santander Bay (Cantabria, northern Spain), a ferromanganese alloy plant is located. Our objective was to characterize the Mn personal exposure of adult healthy volunteers living in this highly Mn exposed region, and to determine its association with a poorer cognitive function.

METHODS

Cross-sectional study analyzing 130 consecutive participants. Cognitive function was assessed by Stroop Color Word, Verbal Fluency tests, Trail Making Test (TMT), Digit Span (WAIS III) and Rey Osterrieth Complex Figure (ROCF) tests and crude scores were standardized according to NEURONORMA norms. Exposure to Mn was assessed in terms of source distance, by Personal Environmental Monitors (PEMs) allowing the separation of fine (PM2.5) and coarse (PM10-2.5) particles (obtaining the bioaccessible fraction by in-vitro bioaccessibility tests), and by biomarkers (blood, hair and fingernails). Age, sex, study level and number of years of residence were predefined as confounding variables and adjusted Mean Differences (MDs) were obtained.

RESULTS

Statistically significant lower scores (negative MDs) in all test were observed when living near the industrial emission source, after adjusting for the predefined variables. Regarding PEMs results, statistically significant lower scores in all Stroop parts were obtained in participants with higher levels of Total Mn in All fractions (PM10). For Verbal Fluency tests, negative MDs were obtained for both bioaccessible fractions. Digit Span Backward scores were lower for those with higher levels in the bioaccessible coarse fraction, and negative MDs were also observed for the ROCF Delayed part and the non-bioaccessible fine fraction. As regards to Mn in fingernails, adjusted MDs of -1.60; 95%CI (-2.57 to -0.64) and -1.45; 95%CI (-2.29 to -0.61) for Digit Span Forward and Backward parts were observed.

CONCLUSIONS

Our results support an association between poorer cognitive function and environmental airborne Mn exposure.

Cognitive impairment and World Trade Centre-related exposures

On 11 September 2001 the World Trade Center (WTC) in New York was attacked by terrorists, causing the collapse of multiple buildings including the iconic 110-story 'Twin Towers'. Thousands of people died that day from the collapse of the buildings, fires, falling from the buildings, falling debris, or other related accidents. Survivors of the attacks, those who worked in search and rescue during and after the buildings collapsed, and those working in recovery and clean-up operations were exposed to severe psychological stressors. Concurrently, these 'WTC-affected' individuals breathed and ingested a mixture of organic and particulate neurotoxins and pro-inflammogens generated as a result of the attack and building collapse. Twenty years later, researchers have documented neurocognitive and motor dysfunctions that resemble the typical features of neurodegenerative disease in some WTC responders at midlife. Cortical atrophy, which usually manifests later in life, has also been observed in this population. Evidence indicates that neurocognitive symptoms and corresponding brain atrophy are associated with both physical exposures at the WTC and chronic post-traumatic stress disorder, including regularly re-experiencing traumatic memories of the events while awake or during sleep. Despite these findings, little is understood about the long-term effects of these physical and mental exposures on the brain health of WTC-affected individuals, and the potential for neurocognitive disorders. Here, we review the existing evidence concerning neurological outcomes in WTC-affected individuals, with the aim of contextualizing this research for policymakers, researchers and clinicians and educating WTC-affected individuals and their friends and families. We conclude by providing a rationale and recommendations for monitoring the neurological health of WTC-affected individuals.

Environmental manganese exposure and cognitive control in a South African population

OBJECTIVE

To characterize the association between environmental (residential air) manganese (Mn) exposure and cognitive performance, focusing on cognitive control, in a Black African population.

METHODS

We administered the Go-No-Go, Digit Span, and Matrix Reasoning tests to population-based samples age ≥40 from a high Mn (smelter) exposed community, Meyerton (N = 629), and a demographically comparable low (background levels) non-exposed community, Ethembalethu, (N = 96) in Gauteng province, South Africa. We investigated the associations between community and performance on the cognitive tests, using linear regression. We adjusted a priori for age and sex, and examined the effect of adjustment for education, nonverbal IQ, smoking, and alcohol consumption. We measured airborne PM_2.5-Mn to confirm community exposure differences.

RESULTS

Compared to Ethembalethu residents, Meyerton residents' test scores were lower (poorer) for all tests: 0.55 (95 % confidence interval [CI] 0.08, 1.03) lower scores for Matrix Reasoning, 0.34 (95 % CI -0.07, 0.75) lower for Digit Span, and 0.15 (95 % CI 0.09, 0.21) lower for Go-No-Go (high frequency discriminability index [probability]). The latter represented the most marked difference in terms of z-scores (0.50, 95 % CI 0.30, 0.71 standard deviations lower). The mean of the z-score of each of the three tests was also lower (0.34, 95 % CI 0.18, 0.50 standard deviations lower). These associations were similar in men and women, but attenuated with adjustment for education. Differences for Matrix Reasoning and Digit Span between the two communities were observed only among those who had lived in Meyerton ≥10 years, whereas for Go-No-Go, differences were also apparent among those who had lived in Meyerton <10 years. Mean PM_2.5-Mn at a long-term fixed site in Meyerton was 203 ng/m³ and 10 ng/m³ in Ethembalethu.

CONCLUSION

Residence in a community near a high Mn emission source is associated with cognitive dysfunction, including aspects of cognitive control as assessed by the Go-No-Go test.

Biomonitoring and bioaccessibility of environmental airborne manganese in relation to motor function in a healthy adult population

BACKGROUND/AIM

Santander, the capital of Cantabria, Spain (172,000 inhabitants) is 7 km from an industrial emission source (IES) of Mn located in a 10,000 inhabitants town (Maliaño) (annual air Mn arithmetic mean = 231.8 ng/m³; reference WHO guideline = 150 ng/m³). Our objective was to compare the motor function of adult healthy volunteers living in both places.

METHODS

Cross-sectional study analyzing 130 consecutive participants. Exposure to Mn was assessed in terms of source distance from the IES, by Personal Environmental Monitors (PEMs) carried for 24 h by participants consisting of a portable impactor connected to a personal pump, and by biomarkers (blood, hair and fingernails). The impactor allowed the separation of fine (PM2.5) and coarse (PM10-2.5) particles and for each particle size in-vitro bioaccessibility tests with biologically active fluids were performed to separate the soluble (bioaccessible) from the insoluble (non-bioaccessible) fraction. Mean Differences (MDs) adjusted for age, sex, and study level, were obtained for motor function tests results.

RESULTS

Regarding Grooved Pegboard, overall mean time to complete the test was 59.31 and 65.27 seconds (Standard Deviation = 10.11 and 11.69) for dominant and nondominant hands respectively. Statistically significant higher times (indicating worse function) were observed when living near the IES in both hands but MDs of only 1.22 and 2.05 seconds were obtained after adjusting for the predefined confounders (p = 0.373 and 0.221 respectively). Regarding Mn levels in their PEMs (in both bioaccessible and non-bioaccessible coarse&fine fractions) higher times were computed in participants with higher levels for the bioaccessible-fine fraction, with a MD that diminished but still yielded statistical significance after controlling for confounding: adjusted MD = 3.01 more seconds; 95%CI (0.44-5.38), p = 0.022. Poorer results were also observed for fingernails levels. Regarding Finger Tapping Test, no statistically significant differences were found with the exception of Mn fingernails levels.

CONCLUSIONS

Our results suggest poorer motor function as assessed by Grooved Pegboard test in relation to "proximity to IES", "bioaccessible-fine fraction as determined by PEMs and "Mn fingernails levels". However, our findings were affected by confounding, and only the adjusted MD for the Mn bioaccessible-fine fraction remained of sufficient magnitude to maintain statistical significance.

Effects of low-dose methylcyclopentadienyl manganese tricarbonyl-derived manganese on the development of diencephalic dopaminergic neurons in zebrafish

Fuel additive methylcyclopentadienyl manganese tricarbonyl (MMT) is counted as an organic manganese (Mn)-derived compound. The toxic effects of Mn (alone and complexed) on dopaminergic (DA) neurotransmission have been investigated in both cellular and animal models. However, the impact of environmentally relevant Mn exposure on DA neurodevelopment is rather poorly understood. In the present study, the MMT dose of 100 μM (about 5 mg Mn/L) caused up-regulation of DA-related genes in association with cell body swelling and increase in the number of DA neurons of the ventral diencephalon subpopulation DC2. Furthermore, our analysis identified significant brain Mn bioaccumulation and enhancement of total dopamine levels in association with locomotor hyperactivity. Although DA levels were restored at adulthood, we observed a deficit in the acquisition and consolidation of memory. Collectively, these findings suggest that developmental exposure to low-level MMT-derived Mn is responsible for the selective alteration of diencephalic DA neurons and with long-lasting effects on fish explorative behaviour in adulthood.

Association between social determinants of health and olfactory function: a scoping review

BACKGROUND

Social determinants of health (SDoH) include the socioeconomic, demographic, and social conditions that influence differences in health status among individuals and groups. The impact of these conditions on olfactory function remains poorly understood. In this scoping review, we systematically review the available literature to synthesize the association between SDoH and olfactory function.

METHODS

In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Review (PRISMA-ScR) guidelines, we performed systematic search queries in PubMed, Embase, and Ovid databases and categorized articles according to themes that emerged regarding SDoH. The primary outcomes included self-reported and objective measurements of smell.

RESULTS

We identified 722 unique references that underwent title and abstract review by two independent reviewers, with 70 articles undergoing full-text review and 57 relevant for data extraction. Six themes emerged in our review, under which we categorized the studies and synthesized respective associations with olfactory function. These include studies exploring socioeconomic status (n = 19, 33%), education status (n = 27, 47%), occupational exposures (n = 26, 46%), racial/ethnic disparities (n = 12, 21%), and lifestyle/behavioral factors (n = 33, 58%).

CONCLUSIONS

Within the context of this scoping review, olfactory dysfunction is significantly more prevalent in patients with lower socioeconomic status, exposure to environmental and occupational toxins, and of minority race/ethnicity, whereas the associations between olfactory dysfunction and education level and lifestyle factors such as smoking and drinking seem to be much more elusive. This review highlights the importance of accounting for SDoH in observational studies examining olfactory outcomes. Given the increased awareness of olfactory loss, special consideration should be given to understanding olfactory dysfunction in the context of these factors.

Influence of manganese exposure on cognitive function, plasma APP and Aβ levels in older men

BACKGROUND

Elevated manganese (Mn) exposure impairs cognition in adults and children, but the association between Mn and cognitive function in elderly people is unclear. Previous studies have linked Mn neurotoxicity in AD to Aβ-dependent mechanisms. However, the association between Mn and plasma APP and Aβ in the general elderly population remains unknown. This study aimed to investigate the association between Mn exposure and cognitive function, plasma APP and plasma Aβ in older adults.

METHODS

Cognitive abilities in 375 men aged 60 and older in Guangxi, China were assessed using the Mini-Mental State Examination (MMSE) and cognitive impairment were identified using education-stratified cut-off points of MMSE scores. Urinary Mn levels and plasma APP, and Aβ levels were measured using ICP-MS and ELISA, respectively.

RESULTS

A total of 109 (29.07 %) older men were identified as having cognitive impairment. The median urinary Mn level was 0.22 μg/g creatinine. Urinary Mn levels were negatively correlated with MMSE scores (β = -1.35, 95 % CI: -2.65 to -0.06; p = 0.041). In addition, higher concentrations of urinary manganese were associated with a greater risk of cognitive impairment (OR = 2.03, 95 % CI: 1.14-3.59; comparing the highest and lowest manganese; p = 0.025). Moreover, plasma APP levels were inversely associated with urinary Mn levels (r = -0.123, p = 0.020), and positively associated with MMSE scores (r = 0.158, p = 0.002). Surprisingly, no correlations were observed between plasma Aβ42, Aβ40, Aβ40/Aβ42, or Aβ42/Aβ40 and urinary Mn levels and MMSE scores.

CONCLUSION

These results suggested that Mn exposure is negatively associated with older men's cognition and plasma APP levels, but not plasma Aβ levels.

Chemosensory Dysfunction Induced by Environmental Pollutants and Its Potential As a Novel Neurotoxicological Indicator: A Review

Air pollution composed of the complex interactions among particular matter, chemicals, and pathogens is an emerging and global environmental issue that closely correlates with a variety of diseases and adverse health effects, especially increasing incidences of neurodegenerative diseases. However, as one of the prevalent health outcomes of air pollution, chemosensory dysfunction has not attracted enough concern until recently. During the COVID-19 pandemic, multiple scientific studies emphasized the plausibly essential roles of the chemosensory system in the airborne transmission airway of viruses into the human body, which can also be utilized by pollutants. In this Review, in addition to summarizing current progress regarding the contributions of traditional air pollutants to chemosensory dysfunction, we highlight the roles of emerging contaminants. We not only sum up clarified mechanisms, such as inflammation and apoptosis but also discuss some not yet completely identified mechanisms, e.g., disruption of olfactory signal transduction. Although the existing evidence is not overwhelming, the chemosensory system is expected to be a useful indicator in neurotoxicology and neural diseases based on accumulating studies that continually excavate the deep link between chemosensory dysfunction and neurodegenerative diseases. Finally, we argue the importance of studies concerning chemosensory dysfunction in understanding the health effects of air pollution and provide comments for some future directions of relevant research.

AERMOD modeling of ambient manganese for residents living near a ferromanganese refinery in Marietta, OH, USA

Elevated exposure to ambient manganese (Mn) is associated with adverse health outcomes. In Marietta, Ohio, the primary source of ambient Mn exposure is from the longest operating ferromanganese refinery in North America. In this study, the US EPA air dispersion model, AERMOD, was used to estimate ambient air Mn levels near the refinery for the years 2008-2013. Modeled air Mn concentrations for 2009-2010 were compared to concentrations obtained from a stationary air sampler. Census block population data were used to estimate population sizes exposed to an annual average air Mn > 50 ng/m3, the US EPA guideline for chronic exposure, for each year. Associations between modeled air Mn, measured soil Mn, and measured indoor dust Mn in the modeled area were also examined. Median modeled air Mn concentrations ranged from 6.3 to 43 ng/m3 across the years. From 12,000-56,000 individuals, including over 2000 children aged 0-14 years, were exposed to respirable annual average ambient air Mn levels exceeding 50 ng/m3 in five of the six years. For 2009-2010, the median modeled air Mn concentration at the stationary site was 20 ng/m3, compared to 18 ng/m3 measured with the stationary air sampler. All model performance measures for monthly modeled concentrations compared to measured concentrations were within acceptable limits. The study shows that AERMOD modeling of ambient air Mn is a viable method for estimating exposure from refinery emissions and that the Marietta area population was at times exposed to Mn levels that exceeded US EPA guidelines.

Characterization and within-site variation of environmental metal concentrations around a contaminated site using a community-engaged approach

Historic industrial activity led to extensive lead and arsenic contamination within residential areas of East Chicago, Indiana, United States. Although remediation is underway, community concerns about this contamination remain. Therefore, the goal for this analysis was to characterize environmental contamination in soil within and around these areas. A total of 228 samples from 32 different sites (addresses) were collected by community members or study staff. These were analyzed for metals using portable x-ray fluorescence or inductively coupled plasma ̶ optical emission spectroscopy. Concentrations exceeding EPA screening levels were found for 42% of the soil arsenic samples, 35% of the soil lead samples, and 79% of the soil manganese samples; a few samples also contained elevated copper or zinc. Concentrations above EPA screening levels were identified both within and outside of the formally designated contaminated area. Roughly 30% of all sites had at least one sample above and one sample below the screening level for arsenic, lead, and manganese. For sites within the contaminated area, more than 90% (arsenic), 60% (lead) and 60% (manganese) of the samples exceeded EPA screening levels. There was a significant association of proximity to the historic industrial site with elevated soil concentrations of arsenic and lead; a similar association was present for manganese. These results are consistent with existing data for lead and arsenic and we additionally report elevated concentrations of manganese and a high within-site variability of all metal concentrations. These findings should be considered in future remediation efforts.

Evaluating the risk of manganese-induced neurotoxicity of parenteral nutrition: review of the current literature

INTRODUCTION

Several diseases and clinical conditions can affect enteral nutrition and adequate gastrointestinal uptake. In this respect, parenteral nutrition (PN) is necessary for the provision of deficient trace elements. However, some essential elements, such as manganese (Mn) may be toxic to children and adults when parenterally administered in excess, leading to toxic, especially neurotoxic effects.

AREAS COVERED

Here, we briefly provide an overview on Mn, addressing its sources of exposure, the role of Mn in the etiology of neurodegenerative diseases, and focusing on potential mechanisms associated with Mn-induced neurotoxicity. In addition, we discuss the potential consequences of overexposure to Mn inherent to PN.

EXPERT OPINION

In this critical review, we suggest that additional research is required to safely set Mn levels in PN, and that eliminating Mn as an additive should be considered by physicians and nutritionists on a case by case basis in the meantime to avoid the greater risk of neurotoxicity by its presence. There is a need to better define clinical biomarkers for Mn toxicity by PN, as well as identify new effective agents to treat Mn-neurotoxicity. Moreover, we highlight the importance of the development of new guidelines and practice safeguards to protect patients from excessive Mn exposure and neurotoxicity upon PN administration.

Impact of Environmental Airborne Manganese Exposure on Cognitive and Motor Functions in Adults: A Systematic Review and Meta-Analysis

Background/Objective: Whether environmental exposure to Manganese (Mn) in adults is associated with poorer results in cognitive and motor function is unclear. We aimed to determine these associations through a meta-analysis of published studies. Methods: A systematic review was conducted to identify epidemiological studies on a population ≥18 years old exposed to environmental airborne Mn, and in which results on specific tests to evaluate cognitive or motor functions were reported. We consulted Medline through PubMed, Web of Science and SCOPUS databases. We also performed a manual search within the list of bibliographic references of the retrieved studies and systematic reviews. To weight Mn effects, a random effects versus fixed effect model was chosen after studying the heterogeneity of each outcome. Results. Eighteen studies met the inclusion criteria. Among them, eleven studies reported data susceptible for meta-analysis through a pooled correlation or a standardized means difference (SMD) approach between exposed and non-exposed groups. Regarding cognitive function, the results of the studies showed heterogeneity among them (I² = 76.49%, p < 0.001). The overall effect was a statistically significant negative correlation in the random effects model (pooled r = −0.165; 95%CI: −0.214 to −0.116; p < 0.001). For SMD, the results showed a lower heterogeneity with a negative SMD that did not reach statistical significance under the fixed effects model (SMD = −0.052; 95%CI −0.108 to 0.004; p = 0.068). Regarding motor function, heterogeneity (I² = 75%) was also observed in the correlation approach with a pooled r (random effect model) = −0.150; 95%CI: −0.219 to −0.079; p < 0.001. Moderate heterogeneity was observed according to the SMD approach (I² = 52.28%), with a pooled SMD = −0.136; 95%CI: −0.188 to−0.084; p < 0.001, indicating worse motor function in those exposed. Conclusions: Correlation approach results support a negative effect on cognitive and motor functions (the higher the Mn levels, the poorer the scores). Regarding the SMD approach, results also support a worse cognitive and motor functions in those exposed, although only for motor function statistical significance was obtained.

Severity of parkinsonism associated with environmental manganese exposure

BACKGROUND

Exposure to occupational manganese (Mn) is associated with neurotoxic brain injury, manifesting primarily as parkinsonism. The association between environmental Mn exposure and parkinsonism is unclear. To characterize the association between environmental Mn exposure and parkinsonism, we performed population-based sampling of residents older than 40 in Meyerton, South Africa (N = 621) in residential settlements adjacent to a large Mn smelter and in a comparable non-exposed settlement in Ethembalethu, South Africa (N = 95) in 2016-2020.

METHODS

A movement disorders specialist examined all participants using the Unified Parkinson Disease Rating Scale motor subsection part 3 (UPDRS3). Participants also completed an accelerometry-based kinematic test and a grooved pegboard test. We compared performance on the UPDRS3, grooved pegboard, and the accelerometry-based kinematic test between the settlements using linear regression, adjusting for covariates. We also measured airborne PM_2.5-Mn in the study settlements.

RESULTS

Mean PM_2.5-Mn concentration at a long-term fixed site in Meyerton was 203 ng/m³ in 2016-2017 - approximately double that measured at two other neighborhoods in Meyerton. The mean Mn concentration in Ethembalethu was ~ 20 times lower than that of the long-term Meyerton site. UPDRS3 scores were 6.6 (CI 5.2, 7.9) points higher in Meyerton than Ethembalethu residents. Mean angular velocity for finger-tapping on the accelerometry-based kinematic test was slower in Meyerton than Ethembalethu residents [dominant hand 74.9 (CI 48.7, 101.2) and non-dominant hand 82.6 (CI 55.2, 110.1) degrees/second slower]. Similarly, Meyerton residents took longer to complete the grooved pegboard, especially for the non-dominant hand (6.9, CI -2.6, 16.3 s longer).

CONCLUSIONS

Environmental airborne Mn exposures at levels substantially lower than current occupational exposure thresholds in the United States may be associated with clinical parkinsonism.

A Review on the Environmental Exposure to Airborne Manganese, Biomonitoring, and Neurological/Neuropsychological Outcomes

The occupational exposure to airborne manganese (Mn) has been linked for decades with neurological effects. With respect to its environmental exposure, the first reviews on this matter stated that the risk posed to human health by this kind of exposure was still unknown. Later, many studies have been developed to analyze the association between environmental Mn exposure and health effects, most of them including the measure of Mn in selected human biomarkers. This review aims at collecting and organizing the literature dealing with the environmental airborne Mn exposure (other routes of exposure were intentionally removed from this review), the biomonitoring of this metal in different body matrices (e.g., blood, urine, nails, hair), and the association between exposure and several adverse health effects, such as, e.g., neurocognitive, neurodevelopmental, or neurobehavioral outcomes. From the different exposure routes, inhalation was the only one considered in this review, to take into account the areas influenced by industrial activities closely related to the Mn industry (ferromanganese and silicomanganese plants, Mn ore mines, and their processing plants) and by traffic in countries where a fuel additive, methylcyclopentadienyl manganese tricarbonyl (MMT), has been used for years. In these areas, high air Mn levels have been reported in comparison with the annual Reference Concentration (RfC) given by the US EPA for Mn, 50 ng/m³. This review was performed using Scopus and MEDLINE databases with a keyword search strategy that took into account that each valid reference should include at least participants that were exposed to environmental airborne Mn and that were subjected to analysis of Mn in biomarkers or subjected to neurological/neuropsychological tests or both. Overall, 47 references matching these criteria were included in the discussion. Most of them report the measure of Mn in selected biomarkers (N = 43) and the assessment of different neurological outcomes (N = 31). A negative association is usually obtained between Mn levels in hair and some neurological outcomes, such as cognitive, motor, olfactory, and emotional functions, but not always significant. However, other biomarkers, such as blood and urine, do not seem to reflect the chronic environmental exposure to low/moderate levels of airborne Mn. Further studies combining the determination of the Mn exposure through environmental airborne sources and biomarkers of exposure and the evaluation of at least cognitive and motor functions are needed to better understand the effects of chronic non-occupational exposure to airborne Mn.

Metal Exposure and SNCA rs356219 Polymorphism Associated With Parkinson Disease and Parkinsonism

Objective: In the province of Brescia, Italy, historical neurotoxic metal exposure has occurred for several decades. This study aimed to explore the role of metal exposure and genetics on Parkinson's Disease (PD) and Parkinsonism. Methods: Cases were enrolled from four local clinics for movement disorders. Randomly selected controls non-affected by neurological or psychiatric conditions were enrolled from the same health centers keeping a similar gender ratio and age distribution as for cases. Data on sociodemographic variables, clinical onset and life habits were collected besides accurate occupational and residential history. Blood samples were collected from all participants for genotyping of target polymorphisms in genes linked to PD and/or metal transport. Results: A total number of 432 cases and 444 controls were enrolled in the study, with average age of 71 years (72.2 for cases and 70 for controls). The average age at diagnosis was 65.9 years (SD 9.9). Among the potential risk factors, family history of PD or Parkinsonism showed the strongest association with the diseases (OR = 4.2, 95% CI 2.3, 7.6 on PD; OR = 4.3, 95% CI 1.9, 9.5 for Parkinsonism), followed by polymorphism rs356219 in the alpha-synuclein (SNCA) gene (OR = 2.03, 95% CI 1.3, 3.3 for CC vs. TT on PD; OR = 2.5, 95% CI 1.1, 5.3 for CC vs. TT on Parkinsonism), exposure to metals (OR = 2.4;, 95% CI 1.3, 4.2 on PD), being born in a farm (OR = 1.8; 95% CI 1.1, 2.8 on PD; OR = 2.6; 95% CI 1.4, 4.9 on Parkinsonism) and being born in the province of Brescia (OR = 1.7; 95% CI 1.0, 2.9 on PD). Conditional OR of having PD depending by SNCA polymorphism and metal exposure highlights higher risk of PD among CC SNCA carriers and being exposed to metals. However, the interaction term was not statistically significant. Conclusions: Lifetime exposure to metals and genetic variation in SNCA gene are relevant determinants of PD and Parkinsonism in the highly industrialized area of Brescia, Italy. The lack of evidence of statistical interaction between environmental and genetic factors may be due to the low frequencies of subjects representing the exposure categories and the polymorphism variants and does not rule out the biological interaction.

The aging brain: impact of heavy metal neurotoxicity

The aging process is accompanied by critical changes in cellular and molecular functions, which upset the homeostatic balance in the central nervous system. Accumulation of metals renders the brain susceptible to neurotoxic insults by mechanisms such as mitochondrial dysfunction, neuronal calcium-ion dyshomeostasis, buildup of damaged molecules, compromised DNA repair, reduction in neurogenesis, and impaired energy metabolism. These hallmarks have been identified to be responsible for neuronal injuries, resulting in several neurological disorders. Various studies have shown solid associations between metal accumulation, abnormal protein expressions, and pathogenesis of neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and Amyotrophic lateral sclerosis. This review highlights metals (such as manganese, zinc, iron, copper, and nickel) for their accumulation, and consequences in the development of neurological disorders, in relation to the aging brain.

Manganese Exposure and Neurologic Outcomes in Adult Populations

A review of published articles examining the effects of manganese exposure to workers and community residents shows adverse neurologic outcomes. Innovative biomarkers, including those from neuroimaging, were incorporated into many of these studies to assess both manganese exposure and neurologic outcomes. A variety of health effects were evaluated, including cognitive and motor impairments. Studies of community participants residing near manganese point sources show variability in outcomes, reflecting the complexities of exposure measurement, individual absorption, and assessment of neurologic effects. The aging population provides insight into the impacts of chronic exposure in younger populations.

Associations of a Metal Mixture Measured in Multiple Biomarkers with IQ: Evidence from Italian Adolescents Living near Ferroalloy Industry

BACKGROUND

Research on the health effects of chemical mixtures has focused mainly on early life rather than adolescence, a potentially important developmental life stage.

OBJECTIVES

We examined associations of a metal mixture with general cognition in a cross-sectional study of adolescents residing near ferromanganese industry, a source of airborne metals emissions.

METHODS

We measured manganese (Mn), lead (Pb), copper (Cu), and chromium (Cr) in hair, blood, urine, nails, and saliva from 635 Italian adolescents 10-14 years of age. Full-scale, verbal, and performance intelligence quotient (FSIQ, VIQ, PIQ) scores were assessed using the Wechsler Intelligence Scale for Children-III. Multivariable linear regression and Bayesian kernel machine regression (BKMR) were used to estimate associations of the metal mixture with IQ. In secondary analyses, we used BKMR's hierarchical variable selection option to inform biomarker selection for Mn, Cu, and Cr.

RESULTS

Median metal concentrations were as follows: hair Mn, 0.08 μ g / g ; hair Cu, 9.6 μ g / g ; hair Cr, 0.05 μ g / g ; and blood Pb, 1.3 μ g / dL . Adjusted models revealed an inverted U-shaped association between hair Cu and VIQ, consistent with Cu as an essential nutrient that is neurotoxic in excess. At low levels of hair Cu (10th percentile, 5.4 μ g / g ), higher concentrations (90th percentiles) of the mixture of Mn, Pb, and Cr (0.3 μ g / g , 2.6 μ g / dL , and 0.1 μ g / g , respectively) were associated with a 2.9 (95% CI: - 5.2 , - 0.5 )-point decrease in VIQ score, compared with median concentrations of the mixture. There was suggestive evidence of interaction between Mn and Cu. In secondary analyses, saliva Mn, hair Cu, and saliva Cr were selected as the biomarkers most strongly associated with VIQ score.

DISCUSSION

Higher adolescent levels of Mn, Pb, and Cr were associated with lower IQ scores, especially at low Cu levels. Findings also support further investigation into Cu as both beneficial and toxic for neurobehavioral outcomes. https://doi.org/10.1289/EHP6803.

The effects of manganese overexposure on brain health

Manganese (Mn) is the twelfth most abundant element on the earth and an essential metal to human health. Mn is present at low concentrations in a variety of dietary sources, which provides adequate Mn content to sustain support various physiological processes in the human body. However, with the rise of Mn utility in a variety of industries, there is an increased risk of overexposure to this transition metal, which can have neurotoxic consequences. This risk includes occupational exposure of Mn to workers as well as overall increased Mn pollution affecting the general public. Here, we review exposure due to air pollution and inhalation in industrial settings; we also delve into the toxic effects of manganese on the brain such as oxidative stress, inflammatory response and transporter dysregulation. Additionally, we summarize current understandings underlying the mechanisms of Mn toxicity.

Skin inflammation induced by ambient particulate matter in China

Most published studies on particulate matter (PM) concerning PM_2.5 and PM₁₀ have focused on PM-induced effects on the respiratory system (particularly lung) and cardiovascular system effects. However, epidemiological and mechanistic studies suggest that PM_2.5 and PM₁₀ also affects the skin, which is a key health issue. In this study, we first reviewed the current status of PM_2.5 and PM₁₀ in China, including relevant regulations, concentration levels, chemical components, and emission sources. Next, we summarized the association between PM_2.5 and PM₁₀ or its representative components, in relation to skin inflammation as well as inflammatory skin diseases, such as atopic dermatitis, acne, eczema, and skin aging. Finally, we determined the mechanism of oxidative stress or programmed cell death induced through PM, which can provide useful information for future research on PM-induced skin inflammation.

Incidence of mild cognitive impairment in World Trade Center responders: Long-term consequences of re-experiencing the events on 9/11/2001

Objective

This study examined whether World Trade Center (WTC) exposures and chronic posttraumatic stress disorder (PTSD) were associated with incidence of mild cognitive impairment (MCI) in a longitudinal analysis of a prospective cohort study of WTC responders.

Methods

Incidence of MCI was assessed in a clinical sample of WTC responders (N = 1800) who were cognitively intact at baseline assessment. Crude incidence rates were calculated and compared to population estimates using standardized incidence ratios. Multivariable analyses used Cox proportional-hazards regression.

Results

Responders were 53.1 years old (SD = 7.9) at baseline. Among eligible cognitively intact responders, 255 (14.2%) developed MCI at follow-up. Incidence of MCI was higher than expected based on expectations from prior published research. Incidence was higher among those with increased PTSD symptom severity, and prolonged exposure was a risk factor in apolipoprotein-ε4 carriers.

Conclusions

PTSD and prolonged WTC exposures were associated with increased incidence of MCI in WTC responders, results that may portend future high rates of dementia in WTC-exposed responders.

Manganese exposure and association with hormone imbalance in children living near a ferro-manganese alloy plant

It has been suggested that manganese (Mn) plays a fundamental role in the reproductive system through interference with the regulation of the secretion of hormones related to puberty. The objective of this study was to evaluate the environmental exposure to Mn and its effects on the endocrine regulation of hormones related to puberty in school-aged children living near a ferro-manganese alloy plant. Toenails, occipital hair, and blood samples were collected from 225 children, between 7 and 12 years of age, in four elementary schools in Simões Filho, Bahia, Brazil, who were exposed to different Mn levels owing to different Mn dust deposition rates. The Mn content was determined in the toenails (MnTn), hair (MnH), and blood (MnB), in addition to blood lead levels (PbB), by using graphite furnace atomic absorption spectrometry. Luteinizing hormone (LH), prolactin (PRL), estradiol (E₂), testosterone (T), and thyroid stimulating hormone (TSH) levels were determined by using a chemiluminescence method. Of the total participants, 50.2% were boys, with an average age of 9 years. PRL values were higher in children attending the school with a higher Mn deposition rate (p < 0.004). We observed that MnTn was positively correlated with PRL levels and exhibited a non-linear association with LH levels. None of the tested Mn biomarkers were associated with E₂, T, or TSH levels. To date, despite several animal studies that have focused on the correlation between Mn exposure and the endocrine regulation of hormones and pubertal development, very few studies have reported a similar relationship between environmental Mn effects and the human endocrine system. Our findings support the hypothesis that elevated exposure to Mn in children may be associated with hormonal imbalances that might trigger the early onset of puberty.

SLC30A10 transporter in the digestive system regulates brain manganese under basal conditions while brain SLC30A10 protects against neurotoxicity

The essential metal manganese becomes neurotoxic at elevated levels. Yet, the mechanisms by which brain manganese homeostasis is regulated are unclear. Loss-of-function mutations in SLC30A10, a cell surface-localized manganese efflux transporter in the brain and liver, induce familial manganese neurotoxicity. To elucidate the role of SLC30A10 in regulating brain manganese, we compared the phenotypes of whole-body and tissue-specific Slc30a10 knockout mice. Surprisingly, unlike whole-body knockouts, brain manganese levels were unaltered in pan-neuronal/glial Slc30a10 knockouts under basal physiological conditions. Further, although transport into bile is a major route of manganese excretion, manganese levels in the brain, blood, and liver of liver-specific Slc30a10 knockouts were only minimally elevated, suggesting that another organ compensated for loss-of-function in the liver. Additional assays revealed that SLC30A10 was also expressed in the gastrointestinal tract. In differentiated enterocytes, SLC30A10 localized to the apical/luminal domain and transported intracellular manganese to the lumen. Importantly, endoderm-specific knockouts, lacking SLC30A10 in the liver and gastrointestinal tract, had markedly elevated manganese levels in the brain, blood, and liver. Thus, under basal physiological conditions, brain manganese is regulated by activity of SLC30A10 in the liver and gastrointestinal tract, and not the brain or just the liver. Notably, however, brain manganese levels of endoderm-specific knockouts were lower than whole-body knockouts, and only whole-body knockouts exhibited manganese-induced neurobehavioral defects. Moreover, after elevated exposure, pan-neuronal/glial knockouts had higher manganese levels in the basal ganglia and thalamus than controls. Therefore, when manganese levels increase, activity of SLC30A10 in the brain protects against neurotoxicity.

Neurotoxic Outcomes of Subchronic Manganese Chloride Exposure via Contaminated Water in Adult Male Rats and the Potential Benefits of Ebselen

The neurological effects of manganese (Mn) exposure on adults consuming contaminated water remain unclear. Accordingly, the current experiment was planned to explore the neurotoxic consequences of subchronic Mn exposure via contaminated water and to examine whether ebselen (Ebs) improved these outcomes. Rats exposed to oral MnCl₂ (50 mg/kg body weight) for 30 successive days exhibited reduced rearing and ambulation. Furthermore, Mn administration increased brain Mn concentrations and induced superoxide dismutase, catalase, and glutathione depletion. Mn administration also increased lipid peroxidation biomarker levels. Additionally, Mn increased interleukin1-β and prostaglandin E2 levels and altered caspase-3 and Bcl-2 expression. Mn intoxication also induced marked gliosis, numerous vacuolations, and disoriented and pyknotic Purkinje cells as well as marked vascular congestion in brain tissue. Meanwhile, intraperitoneal administration of Ebs (15 mg/kg body weight) to Mn-intoxicated rats improved the behavioral performance and oxidative damage as well as inflammatory, apoptotic, and histopathological changes. The above results indicate that Ebs alleviated Mn neurotoxicity via its antioxidant, anti-inflammatory, and anti-apoptotic activities. Therefore, Ebs could represent a promising agent in the prevention of Mn-induced neurotoxicity.

Exposure to Mixtures of Pollutants in Mexican Children from Marginalized Urban Areas

Background:

Exposure to contaminant mixtures in developing countries is an important public health issue. Children are identified as the most susceptible group to adverse health effects due to the exposure.

Objective:

The aim of this study was to conduct a screening for mixture pollutants in Mexican children in urban marginalized communities.

Methods:

We analyzed children (aged 6–12 years old) who resided in four urban marginalized communities in San Luis Potosi, Mexico: i) Bellas Lomas (BEL), a site with vehicular traffic; ii) Tercera Chica (TC), a site with brick kilns; Iii) Rincon de San Jose (SJR), a site with a hazardous waste landfill; and (iv) Morales (MOR) a metallurgical zone with copper-arsenic and electrolytic zinc smelters. Polycyclic Aromatic Hydrocarbons (1-hydroxypyrene (1-OHP)), benzene (trans, trans-muconic acid (t,t-MA), manganese, arsenic and fluoride were quantified in urine and lead in blood samples.

Findings:

Our results indicate that median exposures to manganese were 4.4, 5.2, 5.8 and 6.3 µg/L for BEL, TC, SJR and MOR, respectively. For BEL, fluoride was present at a higher concentration with 2.3 mg/L followed by MOR, TC and SJR with 1.7, 1.5 and 1.2 mg/L respectively. The highest concentrations of arsenic that were found were 11 µg/L in MOR and lead concentration was reported between 4.2 and 6.8 µg/dL, in BEL, TC and MOR. 1-OHP and t,t-MA were higher in TC (0.23 µmol/mol creatinine (cr), 429.7 µg/g cr, respectively) followed by SJR (0.09 µmol/mol cr, 427.4 µg/g cr), MOR (0.03 µmol/mol cr, 258.6 µg/g cr) and BEL (0.06 µmol/mol cr, 220.6 µg/g cr).

Conclusion:

Considering the large number of people, especially children, exposed to multiple pollutants, it is important to design effective intervention programs that reduce exposure and the resultant risk in the numerous urban marginalized communities in Mexico.

Manganese Exposure and Cognition Across the Lifespan: Contemporary Review and Argument for Biphasic Dose-Response Health Effects

Manganese (Mn) is both an essential micronutrient and potential neurotoxicant. This dual role underlies a growing body of literature demonstrating that Mn exhibits a biphasic dose-response relationship with neurocognitive outcomes. We reviewed recent epidemiologic studies from 2007 to 2016 that investigated the relationship between Mn exposure and cognitive outcomes across the lifespan: early life, school-aged children, and adulthood. In total, 27 research articles were included in this review: 12 pediatric and 15 adult studies (10 occupational and five environmental exposures). The majority of these studies provided evidence of the negative effects of Mn exposure on cognition. The pediatric literature provides evidence that both high and low levels of Mn are negatively associated with intellectual development. Future Mn research should include examination of non-linear relationships and multiple neurotoxicants across the lifespan and particularly during critical developmental windows.

Manganese exposure exacerbates progressive motor deficits and neurodegeneration in the MitoPark mouse model of Parkinson's disease: Relevance to gene and environment interactions in metal neurotoxicity

Parkinson's disease (PD) is now recognized as a neurodegenerative condition caused by a complex interplay of genetic and environmental influences. Chronic manganese (Mn) exposure has been implicated in the development of PD. Since mitochondrial dysfunction is associated with PD pathology as well as Mn neurotoxicity, we investigated whether Mn exposure augments mitochondrial dysfunction and neurodegeneration in the nigrostriatal dopaminergic system using a newly available mitochondrially defective transgenic mouse model of PD, the MitoPark mouse. This unique PD model recapitulates key features of the disease including progressive neurobehavioral changes and neuronal degeneration. We exposed MitoPark mice to a low dose of Mn (10mg/kg, p.o.) daily for 4 weeks starting at age 8 wks and then determined the behavioral, neurochemical and histological changes. Mn exposure accelerated the rate of progression of motor deficits in MitoPark mice when compared to the untreated MitoPark group. Mn also worsened olfactory function in this model. Most importantly, Mn exposure intensified the depletion of striatal dopamine and nigral TH neuronal loss in MitoPark mice. The neurodegenerative changes were accompanied by enhanced oxidative damage in the striatum and substantia nigra (SN) of MitoPark mice treated with Mn. Furthermore, Mn-treated MitoPark mice had significantly more oligomeric protein and IBA-1-immunoreactive microglia cells, suggesting Mn augments neuroinflammatory processes in the nigrostriatal pathway. To further confirm the direct effect of Mn on impaired mitochondrial function, we also generated a mitochondrially defective dopaminergic cell model by knocking out the TFAM transcription factor by using a CRISPR-Cas9 gene-editing method. Seahorse mitochondrial bioenergetic analysis revealed that Mn decreases mitochondrial basal and ATP-linked respiration in the TFAM KO cells. Collectively, our results reveal that Mn can augment mitochondrial dysfunction to exacerbate nigrostriatal neurodegeneration and PD-related behavioral symptoms. Our study also demonstrates that the MitoPark mouse is an excellent model to study the gene-environment interactions associated with mitochondrial defects in the nigral dopaminergic system as well as to evaluate the contribution of potential environmental toxicant interactions in a slowly progressive model of Parkinsonism.