Occupational Exposure to Manganese and Fine Motor Skills in Elderly Men: Results from the Heinz Nixdorf Recall Study

The association of bone and blood manganese with motor function in Chinese workers

Manganese (Mn) is an essential element. However, Mn overexposure is associated with motor dysfunction. This cross-sectional study assessed the association between bone Mn (BnMn) and whole blood Mn (BMn) with motor function in 59 Chinese workers. BnMn and BMn were measured using a transportable in vivo neutron activation analysis system and inductively coupled plasma mass spectrometry, respectively. Motor function (manual coordination, postural sway, postural hand tremor, and fine motor function) was assessed using the Coordination Ability Test System (CATSYS) and the Purdue Pegboard. Relationships between Mn biomarkers and motor test scores were analyzed with linear regression models adjusted for age, education, current employment, and current alcohol consumption. BMn was significantly inversely associated with hand tremor intensity (dominant hand (β=-0.04, 95 % confidence interval (CI):-0.07, -0.01; non-dominant hand β=-0.05, 95 % CI:-0.08, -0.01) hand tremor center frequency (non-dominant hand β=-1.61, 95 % CI:-3.03, -0.19) and positively associated with the Purdue Pegboard Assembly Score (β = 4.58, 95 % CI:1.08, 8.07). BnMn was significantly inversely associated with finger-tapping performance (non-dominant hand β=-0.02, 95 % CI:-0.04,-0.004), mean sway (eyes closed and foam β=-0.68, 95 % CI:-1.31,-0.04), and positively associated with hand tremor center frequency (dominant hand, β = 0.40, 95 % CI:0.002, 0.80). These results suggest BMn is related to better postural hand tremor and fine motor control and BnMn is related to worse motor coordination and postural hand tremor but better (i.e., less) postural sway. The unexpected positive results might be explained by choice of biomarker or confounding by work-related motor activities. Larger, longitudinal studies in this area are recommended.

How to Reduce the Exposure of Welders to an Acceptable Level: Results of the InterWeld Study

OBJECTIVES

Workplace measurements in the past have shown that the applicable occupational exposure limits (OELs) are regularly exceeded in practice when high-emission welding processes are applied. The InterWeld pilot study was planned as part of an intervention study to show under which conditions compliance with the OEL is achievable in gas metal arc welding (GMAW) with solid wire. The investigation focussed on local exhaust ventilation, i.e. captor hoods and welding torches with integrated fume extraction.

METHODS

Forty tests with hand-guided GMAW were configured by experts with regard to all technical parameters and carried out by a professional welder. Effects of protective measures and process parameters on the exposure to respirable welding fumes and airborne manganese (Mn), chromium, nickel, and hexavalent chromium were investigated. Personal sampling was carried out in the welder's breathing zone outside the face shield at high flow rates (10 l min-1) in order to achieve sufficient filter loading. Particle masses and welding fume concentrations were determined by weighing the sampling filters. Metal concentrations were analysed by inductive coupled plasma mass spectrometry. In order to evaluate the effects on exposure, the measurements were performed under similar conditions. The data were analysed descriptively and with mixed linear models. For measurements below the limit of detection, the exposure level was estimated using multiple imputation.

RESULTS

Two to five times higher exposures to respirable welding fumes and airborne metals were observed during welding of 10 mm sheets than during welding of 2- or 3-mm sheets. Welding fume and Mn exposure were reduced by 70 and 90% when on-torch extraction or a captor hood was applied. Other airborne metals were reduced to a similar extent. Modifications on welding parameters led to a reduction of exposure against respirable particles by 51 up to 54%.

CONCLUSIONS

Although proper extraction at the point of origin and lower-emitting process variants ensure a drastic reduction in exposure, compliance with current OELs is not guaranteed. In order to ensure adequate health protection, especially at workplaces where thick sheets with long relative arc times are processed, there is a need for technical development.

Short Report: Using Targeted Urine Metabolomics to Distinguish Between Manganese Exposed and Unexposed Workers in a Small Occupational Cohort

Objectives: Despite the widespread use of manganese (Mn) in industrial settings and its association with adverse neurological outcomes, a validated and reliable biomarker for Mn exposure is still elusive. Here, we utilize targeted metabolomics to investigate metabolic differences between Mn-exposed and -unexposed workers, which could inform a putative biomarker for Mn and lead to increased understanding of Mn toxicity. Methods: End of shift spot urine samples collected from Mn exposed (n = 17) and unexposed (n = 15) workers underwent a targeted assay of 362 metabolites using LC-MS/MS; 224 were quantified and retained for analysis. Differences in metabolite abundances between exposed and unexposed workers were tested with a Benjamini-Hochberg adjusted Wilcoxon Rank-Sum test. We explored perturbed pathways related to exposure using a pathway analysis. Results: Seven metabolites were significantly differentially abundant between exposed and unexposed workers (FDR ≤ 0.1), including n-isobutyrylglycine, cholic acid, anserine, beta-alanine, methionine, n-isovalerylglycine, and threonine. Three pathways were significantly perturbed in exposed workers and had an impact score >0.5: beta-alanine metabolism, histidine metabolism, and glycine, serine, and threonine metabolism. Conclusion: This is one of few studies utilizing targeted metabolomics to explore differences between Mn-exposed and -unexposed workers. Metabolite and pathway analysis showed amino acid metabolism was perturbed in these Mn-exposed workers. Amino acids have also been shown to be perturbed in other occupational cohorts exposed to Mn. Additional research is needed to characterize the biological importance of amino acids in the Mn exposure-disease continuum, and to determine how to appropriately utilize and interpret metabolomics data collected from occupational cohorts.

Neuroprotective effects of disubstituted dithiolethione ACDT against manganese-induced toxicity in SH-SY5Y cells

Dithiolethiones are lipophilic, organosulfur compounds that activate the Nrf2 transcription factor causing an upregulation of various phase II antioxidant enzymes. A disubstituted dithiolethione 5-amino-3-thioxo-3H-(1,2) dithiole-4-carboxylic acid ethyl ester (ACDT) retains the functional pharmacophore while also containing modifiable functional groups. Neuroprotection against autoimmune encephalomyelitis in vivo and 6-hydroxy dopamine (a model for Parkinson's disease) in vitro have been previously reported with ACDT. Manganese (Mn) is a metal essential for metabolic processes at low concentrations. Overexposure and accumulation of Mn leads to a neurological condition called manganism which shares pathophysiological sequelae with parkinsonism. Here we hypothesized ACDT to be protective against manganese-induced cytotoxicity. SH-SY5Y human neuroblastoma cells exposed to 300 μM MnCl₂ displayed approximately 50% cell death, and a 24-h pretreatment with 75 μM ACDT significantly reversed this cytotoxicity. ACDT pretreatment was also found to increase total GSH levels (2.18-fold) and the protein levels of NADPH:quinone oxidoreductase-1 (NQO1) enzyme (6.33-fold), indicating an overall increase in the cells' antioxidant defense stores. A corresponding 2.32-fold reduction in the level of Mn-induced reactive oxygen species was also observed in cells pretreated with ACDT. While no changes were observed in the protein levels of apoptotic markers Bax and Bcl-2, pretreatment with 75 μM ACDT led to a 2.09-fold downregulation of ZIP14 import transporter, indicating a potential reduction in the cellular uptake of Mn as an additional neuroprotective mechanism. These effects did not extend to other transporters like the divalent metal transporter 1 (DMT1) or ferroportin. Collectively, ACDT showed substantial neuroprotection against Mn-induced cytotoxicity, opening a path for dithiolethiones as a potential novel therapeutic option against heavy metal neurotoxicity.

Particulate Matter and Associated Metals: A Link with Neurotoxicity and Mental Health

Particulate air pollution (PM) is a mixture of heterogenous components from natural and anthropogenic sources and contributes to a variety of serious illnesses, including neurological and behavioral effects, as well as millions of premature deaths. Ultrafine (PM0.1) and fine-size ambient particles (PM2.5) can enter the circulatory system and cross the blood–brain barrier or enter through the optic nerve, and then upregulate inflammatory markers and increase reactive oxygen species (ROS) in the brain. Toxic and neurotoxic metals such as manganese (Mn), zinc (Zn), lead (Pb), copper (Cu), nickel (Ni), and barium (Ba) can adsorb to the PM surface and potentially contribute to the neurotoxic effects associated with PM exposure. Epidemiological studies have shown a negative relationship between exposure to PM-associated Mn and neurodevelopment amongst children, as well as impaired dexterity in the elderly. Inhaled PM-associated Cu has also been shown to impair motor performance and alter basal ganglia in schoolchildren. This paper provides a brief review of the epidemiological and toxicological studies published over the last five years concerning inhaled PM, PM-relevant metals, neurobiology, and mental health outcomes. Given the growing interest in mental health and the fact that 91% of the world’s population is considered to be exposed to unhealthy air, more research on PM and PM-associated metals and neurological health is needed for future policy decisions and strategic interventions to prevent public harm.

Association of exposure to manganese and fine motor skills in welders - Results from the WELDOX II study

The aim of this study was to evaluate the effect of exposure to manganese (Mn) on fine motor functions. A total of 48 welders and 30 unexposed workers as controls completed questionnaires, underwent blood examinations, and a motor test battery. The shift exposure of welders to respirable Mn was measured with personal samplers. For all subjects accumulations of Mn in the brain were assessed with T1-weighted magnetic resonance imaging. Welders showed normal motor functions on the Movement Disorder Society-Sponsored Revision of the Unified Parkinson Disease Rating Scale part III. Furthermore welders performed excellent on a steadiness test, showing better results than controls. However, welders were slightly slower than controls in motor tests. There was no association between fine motor test results and the relaxation rates R1 in globus pallidus and substantia nigra as MRI-based biomarkers to quantify Mn deposition in the brain.

The Functions of ZIP8, ZIP14, and ZnT10 in the Regulation of Systemic Manganese Homeostasis

As an essential nutrient, manganese is required for the regulation of numerous cellular processes, including cell growth, neuronal health, immune cell function, and antioxidant defense. However, excess manganese in the body is toxic and produces symptoms of neurological and behavioral defects, clinically known as manganism. Therefore, manganese balance needs to be tightly controlled. In the past eight years, mutations of genes encoding metal transporters ZIP8 (SLC39A8), ZIP14 (SLC39A14), and ZnT10 (SLC30A10) have been identified to cause dysregulated manganese homeostasis in humans, highlighting the critical roles of these genes in manganese metabolism. This review focuses on the most recent advances in the understanding of physiological functions of these three identified manganese transporters and summarizes the molecular mechanisms underlying how the loss of functions in these genes leads to impaired manganese homeostasis and human diseases.

Impairment of Motor Function Correlates with Neurometabolite and Brain Iron Alterations in Parkinson's Disease

We took advantage of magnetic resonance imaging (MRI) and spectroscopy (MRS) as non-invasive methods to quantify brain iron and neurometabolites, which were analyzed along with other predictors of motor dysfunction in Parkinson’s disease (PD). Tapping hits, tremor amplitude, and the scores derived from part III of the Movement Disorder Society-Sponsored Revision of the Unified Parkinson Disease Rating Scale (MDS-UPDRS3 scores) were determined in 35 male PD patients and 35 controls. The iron-sensitive MRI relaxation rate R2* was measured in the globus pallidus and substantia nigra. γ-aminobutyric acid (GABA)-edited and short echo-time MRS was used for the quantification of neurometabolites in the striatum and thalamus. Associations of R2*, neurometabolites, and other factors with motor function were estimated with Spearman correlations and mixed regression models to account for repeated measurements (hands, hemispheres). In PD patients, R2* and striatal GABA correlated with MDS-UPDRS3 scores if not adjusted for age. Patients with akinetic-rigid PD subtype (N = 19) presented with lower creatine and striatal glutamate and glutamine (Glx) but elevated thalamic GABA compared to controls or mixed PD subtype. In PD patients, Glx correlated with an impaired dexterity when adjusted for covariates. Elevated myo-inositol was associated with more tapping hits and lower MDS-UPDRS3 scores. Our neuroimaging study provides evidence that motor dysfunction in PD correlates with alterations in brain iron and neurometabolites.