Chronic Mn Exposure Research Articles

Manganese exposure from spring and well waters in the Shenandoah Valley: interplay of aquifer lithology, soil composition, and redox conditions

Manganese (Mn) is of particular concern in groundwater, as low-level chronic exposure to aqueous Mn concentrations in drinking water can result in a variety of health and neurodevelopmental effects. Much of the global population relies on drinking water sourced from karst aquifers. Thus, we seek to assess the relative risk of Mn contamination in karst by investigating the Shenandoah Valley, VA region, as it is underlain by both karst and non-karst aquifers and much of the population relies on water wells and spring water. Water and soil samples were collected throughout the Shenandoah Valley, to supplement pre-existing well water and spring data from the National Water Information System and the Virginia Household Water Quality Program, totaling 1815 wells and 119 springs. Soils were analyzed using X-ray fluorescence and Mn K-Edge X-ray absorption near-edge structure spectroscopy. Factors such as soil type, soil geochemistry, and aquifer lithology were linked with each location to determine if correlations exist with aqueous Mn concentrations. Analyzing the distribution of Mn in drinking water sources suggests that water wells and springs within karst aquifers are preferable with respect to chronic Mn exposure, with < 4.9% of wells and springs in dolostone and limestone aquifers exceeding 100 ppb Mn, while sandstone and shale aquifers have a heightened risk, with > 20% of wells exceeding 100 ppb Mn. The geochemistry of associated soils and spatial relationships to various hydrologic and geologic features indicates that water interactions with aquifer lithology and soils contribute to aqueous Mn concentrations. Relationships between aqueous Mn in spring waters and Mn in soils indicate that increasing aqueous Mn is correlated with decreasing soil Mn(IV). These results point to redox conditions exerting a dominant control on Mn in this region.

Multi-omics analysis reveals Mn exposure affects ferroptosis pathway in zebrafish brain

Manganese (Mn) accumulates in the central nervous system and can cause neurotoxicity, but the mechanisms of Mn-induced neurotoxicity remain unclear. We performed single-cell RNA sequencing (scRNA-seq) of zebrafish brain after Mn exposure and identified 10 cell types by marker genes: cholinergic neurons, dopaminergic (DA) neurons, glutaminergic neurons, GABAergic neurons, neuronal precursors, other neurons, microglia, oligodendrocyte, radial glia, and undefined cells. Each cell type has its distinct transcriptome profile. Pseudotime analysis revealed that DA neurons had a critical role in Mn-induced neurological damage. Combined with metabolomic data, chronic Mn exposure significantly impaired amino acid and lipid metabolic processes in the brain. Furthermore, we found that Mn exposure disrupted the ferroptosis signaling pathway in the DA neurons in zebrafish. Overall, our study employed joint analysis of multi-omics and revealed ferroptosis signaling pathway is a novel potential mechanism of Mn neurotoxicity.

Gray matter microstructural alterations in manganese-exposed welders: a preliminary neuroimaging study.

Chronic occupational manganese (Mn) exposure is characterized by motor and cognitive dysfunction. This study aimed to investigate structural abnormalities in Mn-exposed welders compared to healthy controls (HCs). Thirty-five HCs and forty Mn-exposed welders underwent magnetic resonance imaging (MRI) scans in this study. Based on T1-weighted MRI, the voxel-based morphometry (VBM), structural covariance, and receiver operating characteristic (ROC) curve were applied to examine whole-brain structural changes in Mn-exposed welders. Compared to HCs, Mn-exposed welders had altered gray matter volume (GMV) mainly in the medial prefrontal cortex, lentiform nucleus, hippocampus, and parahippocampus. ROC analysis indicated the potential highest classification power of the hippocampus/parahippocampus. Moreover, distinct structural covariance patterns in the two groups were associated with regions, mainly including the thalamus, insula, amygdala, sensorimotor area, and middle temporal gyrus. No significant relationships were found between the findings and clinical characteristics. Our findings showed Mn-exposed welders had changed GMV and structural covariance patterns in some regions, which implicated in motivative response, cognitive control, and emotional regulation. These results might provide preliminary evidence for understanding the pathophysiology of Mn overexposure. • Chronic Mn exposure might be related to abnormal brain structural neural mechanisms. • Mn-exposed welders had morphological changes in brain regions implicated in emotional modulation, cognitive control, and motor-related response. • Altered gray matter volume in the hippocampus/parahippocampus and putamen might serve as potential biomarkers for Mn overexposure.

YAC128 mouse model of Huntington disease is protected against subtle chronic manganese (Mn)-induced behavioral and neuropathological changes

Manganese (Mn) is an essential micronutrient but excessive levels induce neurotoxic effects. Increasing evidence suggests a deficit of bioavailable Mn in Huntington disease (HD), an inherited neurodegenerative disease characterized by motor and cognitive disturbances. Previous studies have shown rescue of some molecular HD phenotypes by acute Mn exposure. This study simultaneously examined the potential for chronic Mn exposure to attenuate HD behavioral phenotypes, and for the HD genotype to offer protection against detrimental effects of chronic Mn exposure. In two independent studies a chronic Mn exposure paradigm was implemented in the YAC128 mouse model of HD and behavior was assessed at several timepoints. Study 1 exposed WT and YAC128 mice to twice weekly subcutaneous injections of 0, 5, 15, or 50 mg/kg MnCl[2] tetrahydrate from 12 to 32 weeks of age. A promising protective effect against motor coordination decline in 5 mg/kg MnCl[2] tetrahydrate-treated YAC128 mice was detected. Study 2 thus exposed WT and YAC128 mice to either 0 or 5 mg/kg MnCl[2] tetrahydrate from 12 to 52 weeks of age (with a partial randomized treatment crossover at 31 weeks). The same protective effect was not observed under these conditions at higher statistical power. We report subtle toxicological changes in exploratory behavior and total activity induced by chronic Mn exposure in WT mice only, despite similar total increases in brain Mn in WT and YAC128 mice. Further, chronic Mn treatment resulted in a 10–12 % decrease in striatal NeuN positive cell density in WT mice but not YAC128 mice, despite vehicle cell counts already being reduced compared to WT mice as expected for the HD genotype. The subtle changes observed in specific outcome measures, but not others, following long-term low-level Mn exposure in WT mice delineate the neurobehavioral and neuropathological effects at the threshold of chronic Mn toxicity. We conclude that these chronic low-dose Mn exposures do not significantly rescue behavioral HD phenotypes, but YAC2128 mice are protected against the subtle Mn-induced behavioral changes and decreased striatal neuron density observed in Mn-exposed WT mice.

Defective Mitochondrial Dynamics Underlie Manganese-Induced Neurotoxicity.

Perturbations in mitochondrial dynamics have been observed in most neurodegenerative diseases. Here, we focus on manganese (Mn)-induced Parkinsonism-like neurodegeneration, a disorder associated with the preferential of Mn in the basal ganglia where the mitochondria are considered an early target. Despite the extensive characterization of the clinical presentation of manganism, the mechanism by which Mn mediated mitochondrial toxicity is unclear. In this study we hypothesized whether Mn exposure alters mitochondrial activity, including axonal transport of mitochondria and mitochondrial dynamics, morphology, and network. Using primary neuron cultures exposed to 100 μM Mn (which is considered the threshold of Mn toxicity in vitro) and intraperitoneal injections of MnCl2 (25mg/kg) in rat, we observed that Mn increased mitochondrial fission mediated by phosphorylation of dynamin-related protein-1 at serine 616 (p-s616-DRP1) and decreased mitochondrial fusion proteins (MFN1 and MFN2) leading to mitochondrial fragmentation, defects in mitochondrial respiratory capacity, and mitochondrial ultrastructural damage in vivo and in vitro. Furthermore, Mn exposure impaired mitochondrial trafficking by decreasing dynactin (DCTN1) and kinesin-1 (KIF5B) motor proteins and increasing destabilization of the cytoskeleton at protein and gene levels. In addition, mitochondrial communication may also be altered by Mn exposure, increasing the length of nanotunnels to reach out distal mitochondria. These findings revealed an unrecognized role of Mn in dysregulation of mitochondrial dynamics providing a potential explanation of early hallmarks of the disorder, as well as a possible common pathway with neurological disorders arising upon chronic Mn exposure.

Manganese Exposure Aggravates β-Amyloid Pathology by Microglial Activation

Human epidemiological evidence and animal experimental data suggest that chronic manganese (Mn) exposure increases the risk of Alzheimer’s disease (AD) and amyloid plaques, a hallmark of AD brain pathology, but the underlying mechanisms were not fully understood. Using the transgenic APP/PS1/Tau triple transgenic AD (3×Tg-AD) mouse model and mouse-derived microglia and neuroblastoma cell lines, we found that chronic 5-month Mn treatment increased beta amyloid peptide (Aβ) expression and Aβ plaques in the cerebral cortex and hippocampus in these 3×Tg-AD mice. Furthermore, we found that the β- and γ-secretase cleavage activities were markedly increased, while α-secretase cleavage activity was reduced in the brain of Mn-treated AD mice; these effects increase Aβ production and thus are amyloidogenic. Equally important, Mn treatment alone did not alter β-secretase 1 (BACE1) gene expression or Aβ production in amyloidogenic mutant amyloid precursor protein (APP) gene hAPPsw-transfected N2a cells (APPsw-N2a), but in APPsw-N2a cells either co-cultured with microglia or cultured with microglia-conditioned media, Mn exposure increased BACE1 expression and amyloidogenesis. We further determined that Mn exposure promoted the activation of microglia both in 3×Tg-AD mouse brains and in cultured microglia cells, and increased the secretion of the inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). Taken together, these results suggest that Mn may increase the release of IL-1β and TNF-α from microglia that in turn stimulates the expression of BACE1 gene and protein and consequently Aβ production; this novel molecular mechanism not only advances our understanding about the amyloidogenic effect of chronic Mn exposure reported for special human populations but also indicates Mn dyshomeostasis as a potential contributor to AD pathogenesis.

Chronic Manganese Administration with Longer Intervals Between Injections Produced Neurotoxicity and Hepatotoxicity in Rats.

Subacute exposure to manganese (Mn) produced Parkinson’s disease-like syndrome called Manganism. Chronic onset and progression are characteristics of Manganism, therefore, this study aimed to examine Mn toxicity following chronic exposures. Male Sprague-Dawley rats were injected Mn2+ 1 and 5 mg/kg, every 10 days for 150 days (15 injections). Animal body weight and behavioral activities were recorded. At the end of experiments, the brain and liver were collected for morphological and molecular analysis. Chronic Mn exposure did not affect animal body weight gain, but the high dose of Mn treatment caused 20% mortality after 140 days of administration. Motor activity deficits were observed in a dose-dependent manner at 148 days of Mn administration. Immunofluorescence double staining of substantia nigra pars compacta (SNpc) revealed the activation of microglia and loss of dopaminergic neurons. The chronic neuroinflammation mediators TNFα, inflammasome Nlrp3, Fc fragment of IgG receptor IIb, and formyl peptide receptor-1 were increased, implicating chronic Mn-induced neuroinflammation. Chronic Mn exposure also produced liver injury, as evidenced by hepatocyte degeneration with pink, condensed nuclei, indicative of apoptotic lesions. The inflammatory cytokines TNFα, IL-1β, and IL-6 were increased, alone with stress-related genes heme oxygenase-1, NAD(P)H:quinone oxidoreductase-1 and metallothionein. Hepatic transporters, such as multidrug resistant proteins (Abcc1, Abcc2, and Abcc3) and solute carrier family proteins (Slc30a1, Slc39a8 and Slc39a14) were increased in attempt to eliminate Mn from the liver. In summary, chronic Mn exposure produced neuroinflammation and dopaminergic neuron loss in the brain, but also produced inflammation to the liver, with upregulation of hepatic transporters.Graphic

Associations between manganese exposure and multiple immunological parameters in manganese-exposed workers healthy cohort

BackgroundManganese (Mn) ions play a crucial role in the immune response. The immunotoxicity of Mn is rarely reported compared with the neurotoxicity of Mn. ObjectivesThe purpose of this study was to investigate the associations between chronic Mn exposure and immunological parameters in occupational Mn-exposed workers. MethodsA total of 538 workers were selected from the follow-up of manganese-exposed workers healthy cohort (MEWHC) in 2017. We divided the workers into the low-exposure group and the high-exposure group by the cutoff of the manganese-time weighted average (Mn-TWA) setting at 0.15 mg/m3. We examined serum immunological parameters by the immunoturbidimetric method and leukocyte counts and ratios in blood routine. Then we used the generalized linear model analyses and spline analyses to explore the associations between external exposure of Mn and multiple immunological parameters adjusted for variables. Based on the epidemiological analyses, we used Elisa (enzyme-linked immune sorbent assay) to detect plasma complement C3 of Mn-exposed rats. ResultsIn male workers, the mean value of complement C3 was 1.20 ± 0.16 g/L in the high-exposure group, which was significantly lower as compared to the low-exposure group (1.25 ± 0.18 g/L, P = 0.023). The generalize linear models’ analyses showed that complement C3 value had a significantly negative association with external exposure of Mn included adjustment for variables (β = -0.04, P = 0.035). Moreover, in male rats, the high-exposure group also had a lower level of complement C3 compared with the low-exposure group (P < 0.001). None significant association was observed in immunological parameters among female workers and rats (all P > 0.05). ConclusionsMn exposure from inhalable dust was associated with decreased complement C3 among occupationally Mn-exposed male individuals but not in female workers, which was further confirmed by the rat model. Further research into the possible mechanism of C3 reduction is needed in the future.

P.169 The effect of CDNF on N171-82Q mouse model of Huntington`s disease

Manganese (Mn) is an essential micronutrient but excessive levels induce neurotoxic effects. Increasing evidence suggests a deficit of bioavailable Mn in Huntington disease (HD), an inherited neurodegenerative disease characterized by motor and cognitive disturbances. Previous studies have shown rescue of some molecular HD phenotypes by acute Mn exposure. This study simultaneously examined the potential for chronic Mn exposure to attenuate HD behavioral phenotypes, and for the HD genotype to offer protection against detrimental effects of chronic Mn exposure. In two independent studies a chronic Mn exposure paradigm was implemented in the YAC128 mouse model of HD and behavior was assessed at several timepoints. Study 1 exposed WT and YAC128 mice to twice weekly subcutaneous injections of 0, 5, 15, or 50 mg/kg MnCl[2] tetrahydrate from 12 to 32 weeks of age. A promising protective effect against motor coordination decline in 5 mg/kg MnCl[2] tetrahydrate-treated YAC128 mice was detected. Study 2 thus exposed WT and YAC128 mice to either 0 or 5 mg/kg MnCl[2] tetrahydrate from 12 to 52 weeks of age (with a partial randomized treatment crossover at 31 weeks). The same protective effect was not observed under these conditions at higher statistical power. We report subtle toxicological changes in exploratory behavior and total activity induced by chronic Mn exposure in WT mice only, despite similar total increases in brain Mn in WT and YAC128 mice. Further, chronic Mn treatment resulted in a 10–12 % decrease in striatal NeuN positive cell density in WT mice but not YAC128 mice, despite vehicle cell counts already being reduced compared to WT mice as expected for the HD genotype. The subtle changes observed in specific outcome measures, but not others, following long-term low-level Mn exposure in WT mice delineate the neurobehavioral and neuropathological effects at the threshold of chronic Mn toxicity. We conclude that these chronic low-dose Mn exposures do not significantly rescue behavioral HD phenotypes, but YAC2128 mice are protected against the subtle Mn-induced behavioral changes and decreased striatal neuron density observed in Mn-exposed WT mice.

Manganese exposure augments misfolded α‐synuclein‐induced proinflammatory M1 microglial phenotype and inflammasome activation

Sustained microglial activation is a key player in the immunopathogenesis of several neurodegenerative disorders including Parkinson's disease (PD). Chronic exposure to the environmental toxicant manganese (Mn) has been implicated as a risk factor for PD. We have previously demonstrated that misfolded and aggregated human α‐synuclein (αSynPFF) induces microglial activation. Recently, we have shown that chronic Mn exposure induces neuroinflammation by impairing mitochondrial dynamics. In this study, we determined whether Mn exposure alters the specific RNA transcripts in response to the αSynPFF proteostatic challenge. We systematically characterized the transcriptome of mouse microglia in response to Mn and/or αSynPFF using RNA sequencing. Treating a mouse microglial cell model with αSynPFF significantly induced both cytokine and interferon‐g signaling pathways. In contrast, Mn treatment caused distinct changes to pathways related to cellular senescence and apoptosis. Intriguingly, co‐treatment with Mn and αSynPFF caused profound enrichment of transcripts, including IL‐6, IL‐12b, IFN‐β, IL‐1α, and IL‐1β CXCL2, CXCL3, CXCL10, CCL5‐R, and Nos2, that signify the proinflammatory M1 microglial phenotype. These targets were further validated by real‐time qRT‐PCR, immunoblotting, and immunocytochemistry. As anticipated, cotreatment with Mn and αSynPFF lead to significant upregulation of the mRNA expression of IL‐6, Nos2, IL‐1α, and IL‐1β in a synergistic manner when compared to either treatment alone. Additionally, Mn and αSynPFF co‐treatment elicited NLRP3 inflammasome activation when compared to either treatment alone or untreated control cells. Taken together, these findings identify that environmental toxicants, such as Mn, perturb microglial homeostasis, thereby leading to transformation to a pro‐inflammatory M1 microglial phenotypic state. Importantly, our study suggests that the environmental toxicant Mn can augment αSynPFF‐induced neuroinflammatory processes in microglia to accelerate neurodegeneration.Support or Funding InformationNIH grants ES026892, NS088206, and W. Eugene Linda Lloyd Endowed ChairThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

PET imaging of dopamine release in the frontal cortex of manganese-exposed non-human primates.

Humans and non-human primates exposed to excess levels of manganese (Mn) exhibit deficits in working memory and attention. Frontal cortex and fronto-striatal networks are implicated in working memory and these circuits rely on dopamine for optimal performance. Here, we aimed to determine if chronic Mn exposure alters invivo dopamine release (DAR) in the frontal cortex of non-human primates. We used [11 C]-FLB457 positron emission tomography with amphetamine challenge to measure DAR in Cynomolgus macaques. Animals received [11 C]-FLB457 positron emission tomography scans with and without amphetamine challenge prior to Mn exposure (baseline), at different time points during the Mn exposure period, and after 10months of Mn exposure cessation. Four of six Mn-exposed animals expressed significant impairment of frontal cortex invivo DAR relative to baseline. One Mn animal had no change in DAR and another Mn animal expressed increased DAR relative to baseline. In the reversal studies, one Mn-exposed animal exhibited complete recovery of DAR while the second animal had partial recovery. In both animals, frontal cortex Mn concentrations normalized after 10months of exposure cessation based on T1-weighted magnetic resonance imaging. D1-dopamine receptor (D1R) autoradiography in frontal cortex tissue indicates that Mn animals that experienced cessation of Mn exposure expressed D1R levels that were approximately 50% lower than Mn animals that did not experience cessation of Mn exposure or control animals. The present study provides evidence of Mn-induced alterations in frontal cortex DAR and D1R that may be associated with working memory and attention deficits observed in Mn-exposed subjects.

Higher Hippocampal Mean Diffusivity Values in Asymptomatic Welders.

Chronic high-level manganese (Mn)-induced neurotoxicity has been associated with Mn accumulation in the basal ganglia and higher risk for developing parkinsonism. Recent studies in Mn-exposed animals revealed Mn accumulation in the hippocampus, the presence of Aβ diffuse plaques, and deficits in associative learning, the latter being hallmarks of Alzheimer's disease (AD) or related disorders. This and recent evidence of hippocampal Mn accumulation in welders prompted us to test the hypothesis that welders with chronic Mn exposure would display changes in the hippocampus. Subjects with (welders; n = 42) or without (controls; n = 31) welding history were studied. Mn exposure was estimated by occupational questionnaires, whole blood Mn, and R1 imaging (estimate of short-term brain Mn accumulation). Hippocampal diffusion tensor imaging (DTI; estimate of microstructural brain changes) and volume were determined. Compared with controls, welders displayed no significant difference in hippocampal volume (p = .165). Welders, however, exhibited higher DTI hippocampal mean diffusivity (MD) values compared with controls (p = .035) that was evident particularly in older welders (>50 years, p = .002). Hippocampal MD was associated significantly with age in welders (R = 0.59; p < .001) but not in controls (p = .16). Moreover, higher hippocampal MD values (age adjusted) were associated with long-term cumulative Mn exposure (R = 0.36, p = .021). Welders with chronic exposure have higher MD values in the hippocampus that become greater with increasing age, a brain change that is similar to that observed in those at risk for AD. The current results suggest that Mn exposure, coupled with aging, may make welders more vulnerable to AD or AD-like changes.

Manganese causes neurotoxic iron accumulation via translational repression of amyloid precursor protein and H-Ferritin.

For more than 150years, it is known that occupational overexposure of manganese (Mn) causes movement disorders resembling Parkinson's disease (PD) and PD-like syndromes. However, the mechanisms of Mn toxicity are still poorly understood. Here, we demonstrate that Mn dose- and time-dependently blocks the protein translation of amyloid precursor protein (APP) and heavy-chain Ferritin (H-Ferritin), both iron homeostatic proteins with neuroprotective features. APP and H-Ferritin are post-transcriptionally regulated by iron responsive proteins, which bind to homologous iron responsive elements (IREs) located in the 5'-untranslated regions (5'-UTRs) within their mRNA transcripts. Using reporter assays, we demonstrate that Mn exposure repressed the 5'-UTR-activity of APP and H-Ferritin, presumably via increased iron responsive proteins-iron responsive elements binding, ultimately blocking their protein translation. Using two specific Fe2+ -specific probes (RhoNox-1 and IP-1) and ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS), we show that loss of the protective axis of APP and H-Ferritin resulted in unchecked accumulation of redox-active ferrous iron (Fe2+ ) fueling neurotoxic oxidative stress. Enforced APP expression partially attenuated Mn-induced generation of cellular and lipid reactive oxygen species and neurotoxicity. Lastly, we could validate the Mn-mediated suppression of APP and H-Ferritin in two rodent invivo models (C57BL6/N mice and RjHan:SD rats) mimicking acute and chronic Mn exposure. Together, these results suggest that Mn-induced neurotoxicity is partly attributable to the translational inhibition of APP and H-Ferritin resulting in impaired iron metabolism and exacerbated neurotoxic oxidative stress. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

The Impact of Environmental Mn Exposure on Insect Biology.

Manganese (Mn) is an essential trace element that acts as a metal co-factor in diverse biochemical and cellular functions. However, chronic environmental exposure to high levels of Mn is a well-established risk factor for the etiology of severe, atypical parkinsonian syndrome (manganism) via its accumulation in the basal ganglia, pallidum, and striatum brain regions, which is often associated with abnormal dopamine, GABA, and glutamate neural signaling. Recent studies have indicated that chronic Mn exposure at levels that are below the risk for manganism can still cause behavioral, cognitive, and motor dysfunctions via poorly understood mechanisms at the molecular and cellular levels. Furthermore, in spite of significant advances in understanding Mn-induced behavioral and neuronal pathologies, available data are primarily for human and rodents. In contrast, the possible impact of environmental Mn exposure on brain functions and behavior of other animal species, especially insects and other invertebrates, remains mostly unknown both in the laboratory and natural habitats. Yet, the effects of environmental exposure to metals such as Mn on insect development, physiology, and behavior could also have major indirect impacts on human health via the long-term disruptions of food webs, as well as direct impact on the economy because of the important role insects play in crop pollination. Indeed, laboratory and field studies indicate that chronic exposures to metals such as Mn, even at levels that are below what is currently considered toxic, affect the dopaminergic signaling pathway in the insect brain, and have a major impact on the behavior of insects, including foraging activity of important pollinators such as the honey bee. Together, these studies highlight the need for a better understanding of the neuronal, molecular, and genetic processes that underlie the toxicity of Mn and other metal pollutants in diverse animal species, including insects.

In vivo neutron activation analysis of bone manganese in workers

Objective: Manganese (Mn) is a neurotoxin. However, the impact of elevated, chronic Mn exposure is not well understood, partially due to the lack of a cumulative exposure biomarker. To address this gap, our group developed a compact in vivo neutron activation analysis (IVNAA) system to quantify Mn concentration in bone (MnBn). Approach: In this study, we used this system and determined MnBn among male Chinese workers and compared results to their blood Mn (MnB), a measure of recent exposure, and the years of employment, a measure of cumulative exposure. A cross-sectional study was conducted with 30 ferroalloy smelters (exposed) and 30 general manufacturing workers (controls). MnBn was assessed using IVNAA, MnB was measured with inductively coupled plasma mass spectrometry, and occupational history and demographics were obtained via questionnaire. Mn-doped phantoms were used to generate a calibration curve; spectra from these phantoms were consistent with in vivo spectra. Main results: The median (interquartile range (IQR)) values for Mn biomarkers were 2.7 µg g−1 (7.2) for MnBn and 14.1 µg l−1 (4.0) for MnB. In regression models adjusted for age and education, the natural log transformed MnBn (ln(MnBn)) was significantly associated with the exposed/control status (β = 0.44, p = 0.047) and years of employment (β = 0.05, p = 0.002), but not with natural log transformed MnB (ln(MnB)) (β = 0.54, p = 0.188). Significance: Our results support the use of IVNAA to quantify MnBn and the use of MnBn as a biomarker of cumulative Mn exposure.

Thalamic GABA levels and occupational manganese neurotoxicity: Association with exposure levels and brain MRI

Excessive occupational exposure to Manganese (Mn) has been associated with clinical symptoms resembling idiopathic Parkinson’s disease (IPD), impairing cognitive and motor functions. Several studies point towards an involvement of the brain neurotransmitter system in Mn intoxication, which is hypothesized to be disturbed prior to onset of symptoms. Edited Magnetic Resonance Spectroscopy (MRS) offers the unique possibility to measure γ-amminobutyric acid (GABA) and other neurometabolites in vivo non-invasively in workers exposed to Mn. In addition, the property of Mn as Magnetic Resonance Imaging (MRI) contrast agent may be used to study Mn deposition in the human brain. In this study, using MRI, MRS, personal air sampling at the working place, work history questionnaires, and neurological assessment (UPDRS-III), the effects of chronic Mn exposure on the thalamic GABAergic system was studied in a group of welders (N=39) with exposure to Mn fumes in a typical occupational setting. Two subgroups of welders with different exposure levels (Low: N=26; mean air Mn=0.13±0.1mg/m3; High: N=13; mean air Mn=0.23±0.18mg/m3), as well as unexposed control workers (N=22, mean air Mn=0.002±0.001mg/m3) were recruited. The group of welders with higher exposure showed a significant increase of thalamic GABA levels by 45% (p<0.01, F(1,33)=9.55), as well as significantly worse performance in general motor function (p<0.01, F(1,33)=11.35). However, welders with lower exposure did not differ from the controls in GABA levels or motor performance. Further, in welders the thalamic GABA levels were best predicted by past-12-months exposure levels and were influenced by the Mn deposition in the substantia nigra and globus pallidus. Importantly, both thalamic GABA levels and motor function displayed a non-linear pattern of response to Mn exposure, suggesting a threshold effect.

Global DNA methylation profiling of manganese-exposed human neuroblastoma SH-SY5Y cells reveals epigenetic alterations in Parkinson’s disease-associated genes

Manganese (Mn) is an essential trace element required for optimal functioning of cellular biochemical pathways in the central nervous system. Elevated exposure to Mn through environmental and occupational exposure can cause neurotoxic effects resulting in manganism, a condition with clinical symptoms identical to idiopathic Parkinson's disease. Epigenetics is now recognized as a biological mechanism involved in the etiology of various diseases. Here, we investigated the role of DNA methylation alterations induced by chronic Mn (100µM) exposure in human neuroblastoma (SH-SY5Y) cells in relevance to Parkinson's disease. A combined analysis of DNA methylation and gene expression data for Parkinson's disease-associated genes was carried out. Whole-genome bisulfite conversion and sequencing indicate epigenetic perturbation of key genes involved in biological processes associated with neuronal cell health. Integration of DNA methylation data with gene expression reveals epigenetic alterations to PINK1, PARK2 and TH genes that play critical roles in the onset of Parkinsonism. The present study suggests that Mn-induced alteration of DNA methylation of PINK1-PARK2 may influence mitochondrial function and promote Parkinsonism. Our findings provide a basis to further explore and validate the epigenetic basis of Mn-induced neurotoxicity .

Cognitive control dysfunction in workers exposed to manganese-containing welding fume.

Chronic exposure to manganese (Mn) is a health concern in occupations such as welding because of well-established motor effects due to basal ganglia dysfunction. We hypothesized that cognitive control (the ability to monitor, manipulate, and regulate ongoing cognitive demands) would also be affected by chronic Mn exposure. We examined the relationship between Mn exposure and cognitive control performance in 95 workers with varying intensity and duration (median 15.5 years) of exposure to welding fume. We performed linear regression to assess the association between exposure to Mn-containing welding fume and cognitive control tasks. Overall performance was inversely related to intensity of welding exposure (P = 0.009) and was driven by the Two-Back and Letter Number Sequencing tests that assess working memory (both P = 0.02). Occupational exposure to Mn-containing welding fume may be associated with poorer working memory performance, and workers may benefit from practices that reduce exposure intensity. Am. J. Ind. Med. 60:181-188, 2017. © 2016 Wiley Periodicals, Inc.

Editor's Highlight: Lower Fractional Anisotropy in the Globus Pallidus of Asymptomatic Welders, a Marker for Long-Term Welding Exposure.

Welding fumes contain several metals including manganese (Mn), iron (Fe), and copper (Cu) that at high exposure may co-influence welding-related neurotoxicity. The relationship between brain accumulation of these metals and neuropathology, especially in welders with subclinical exposure levels, is unclear. This study examined the microstructural integrity of basal ganglia (BG) regions in asymptomatic welders using diffusion tensor imaging (DTI). Subjects with (n = 43) and without (age- and gender-matched controls; n = 31) history of welding were studied. Occupational questionnaires estimated short-term (HrsW; welding hours and E90; cumulative exposure, past 90 days) and long-term (YrsW; total years welding and ELT; cumulative exposure, lifetime) exposure. Whole blood metal levels (Mn, Fe, and Cu) were obtained. Brain MRI pallidal index (PI), R1 (1/T1), and R2* (1/T2*) were measured to estimate Mn and Fe accumulation in BG [caudate, putamen, and globus pallidus (GP)]. DTI was used to assess BG microstructural differences, and related with exposure measurements. When compared with controls, welders had significantly lower fractional anisotropy (FA) in the GP. In welders, GP FA values showed non-linear relationships to YrsW, blood Mn, and PI. GP FA decreased after a critical level of YrsW or Mn was reached, whereas it decreased with increasing PI values until plateauing at the highest PI values. GP FA, however, did not show any relationship with short-term exposure measurements (HrsW, E90), blood Cu and Fe, or R(2)* values. GP FA captured microstructural changes associated with chronic low-level Mn exposure, and may serve as a biomarker for neurotoxicity in asymptomatic welders.

Manganese-Stimulated Kisspeptin Is Mediated by the IGF-1/Akt/Mammalian Target of Rapamycin Pathway in the Prepubertal Female Rat.

Low-dose administration of manganese chloride (MnCl2) causes release of hypothalamic LH-releasing hormone (LHRH) and advances puberty in rat. Recently, this element was shown to up-regulate mammalian target of rapamycin (mTOR), kisspeptin gene (KiSS-1), and LHRH gene expressions in the brain preoptic area (POA)/anteroventral periventricular (AVPV) nucleus. Because these genes are critical for puberty, this study was conducted to identify the upstream mechanism by which Mn activates the mTOR/KiSS-1 pathway. On day 12, immature female rats began receiving a daily supplemental dose of 10 mg/kg of MnCl2 or saline by gavage, and POA/AVPV tissues were collected on day 29 for specific protein assessments. Another experiment assessed in vitro IGF-1 release in response to Mn and assessed signal transduction pathways in the POA/AVPV region after Mn delivery into the third ventricle. Chronic Mn exposure increased (P < .05) basal expressions of mTOR and kisspeptin proteins. Mn increased protein kinase B (Akt) and Ras homolog enriched in brain, both capable of activating mTOR. Central Mn delivery increased expressions of phosphorylated IGF-1 receptor (IGF-1R) (P < .05) and Akt (P < .01) in the POA/AVPV region. The previous central delivery of JB1, an IGF-1R antagonist, blocked Mn-induced expressions of both phosphorylated IGF-1R and Akt. Downstream to Akt, centrally administered Mn increased tuberous sclerosis complex 2 (P < .05), Ras homolog enriched in brain (P < .01), mTOR (P < .05), and kisspeptin (P < .05). Finally, we observed that the early puberty induced by Mn was blocked by the administration of an mTOR inhibitor. These results suggest that Mn acts, at least in part, through the IGF-1/Akt/mTOR pathway to influence prepubertal kisspeptin and LHRH.