Associations between former exposure to manganese and olfaction in an elderly population: Results from the Heinz Nixdorf Recall Study

Biomarkers for occupational manganese exposure

Long-term inhalation exposure to manganese (Mn) metal or its inorganic compounds can result in manganism or subclinical neurofunctional deficits. Studies have described affected workers in Mn dioxide mining, Mn-containing ore crushing and milling facilities, manufacturing of dry-cell batteries, Mn steel and alloy production plants, and in welders. The objective of this study was to critically review existing evidence on the reliability of potential biomarkers of Mn exposure, specifically the relationship between inhalation exposure to Mn particulates in different occupational settings and Mn concentrations in blood and other biological fluids and tissues, with a particular focus on whole blood as a potentially useful medium for measuring internal tissue dose. We also examined available evidence on the relationship between Mn levels in blood and adverse clinical and subclinical neurotoxic outcomes. Three bibliographic databases were searched for relevant studies and identified references were screened by two independent reviewers. Of the 6338 unique references identified, 76 articles were retained for data abstraction. Findings indicate that the relationships between Mn in blood and both external Mn exposure indices and neurofunctional impairments are limited and inconsistent. Different sources of exposure to Mn compounds, heterogeneity in the methodological approaches, and inadequate reporting of essential information limited direct comparison of the reported findings. Among the Mn-exposure biomarkers considered in this review - including biomarkers in blood, plasma, serum, erythrocytes, urine, bone, toenails, fingernails, hair, saliva - biomarkers in whole blood may provide to be most useful in Mn biomonitoring and risk assessment.

Environmental triggers of Parkinson's disease - Implications of the Braak and dual-hit hypotheses

Idiopathic Parkinson's disease (PD) may take decades to develop, during which many risk or protective factors may come into play to initiate the pathogenesis or modify its progression to clinical PD. The lack of understanding of this prodromal phase of PD and the factors involved has been a major hurdle in the study of PD etiology and preventive strategies. Although still controversial, the Braak and dual-hit hypotheses that PD may start peripherally in the olfactory structures and/or the gut provides a theoretical platform to identify the triggers and modifiers of PD prodromal development and progression. This is particularly true for the search of environmental causes of PD as the olfactory structures and gut are the major human mucosal interfaces with the environment. In this review, we lay out our personal views about how the Braak and dual-hit hypotheses may help us search for the environmental triggers and modifiers for PD, summarize available experimental and epidemiological evidence, and discuss research gaps and strategies.

Re-evaluation of potential predictors of calretinin and mesothelin in a population-based cohort study using assays for the routine application in clinical medicine

OBJECTIVES

Calretinin and mesothelin are molecular markers for the detection of malignant mesothelioma at early stages. Our objective was the re-evaluation of factors influencing calretinin and mesothelin concentrations in plasma of cancer-free men in order to minimise false-positive tests when using commercial assays approved for clinical diagnostics.

SETTING

This re-evaluation used data and archived blood samples of the population-based Heinz Nixdorf Recall Study (HNRS) collected from 2011 to 2014.

PARTICIPANTS

The present analysis comprised of 569 cancer-free men at the time of blood sampling (median age 70 years) from HNRS.

PRIMARY AND SECONDARY OUTCOMES

Mesothelin plasma concentration was determined using ELISA and CLEIA (chemiluminescent enzyme immunoassay). Calretinin plasma concentration was assessed using ELISA.

RESULTS

Compared with the previous determination of concentrations, we detected less false-positive tests using the commercial assays. In this analysis, we found nine false-positive calretinin tests using the ELISA (specificity 98.4%, 95% CI 97.0% to 99.2%) and 24 false-positive mesothelin tests using both ELISA and CLEIA (specificity 95.8%, 95% CI 93.8% to 97.2%). We confirmed renal dysfunction as major predictor of elevated marker concentrations. Mesothelin was additionally affected by bronchitis. Furthermore, elevated inflammation values and hypertension only affected the mesothelin concentration determined by ELISA.

CONCLUSIONS

The newly available assays of calretinin and mesothelin approved for clinical diagnostics showed high specificities in the population-based cohort of elderly men without a malignant disease. The current evaluation provides a basis to consider influencing factors in order to further improve the diagnostic procedure.

Neurotoxicity and Chemoreception: A Systematic Review of Neurotoxicity Effects on Smell and Taste

Several different types of exposure have the potential to produce olfactory and gustatory deficits related to neurotoxicity. Although the literature contains relatively few studies of such chemoreceptive dysfunction in the context of toxic exposure, this review explores the strength of such published associations. Several studies collectively demonstrated moderately strong evidence for an association between manganese dust exposure and olfactory deficits. Evidence of associations between individual chemicals, therapeutics, and composites, such as World Trade Center debris, and olfactory and gustatory deficits remains limited or mixed. Further need for controlled studies for clinical management, exposure limits, and policy development is identified.

The Prevalence of Olfactory Dysfunction in the General Population: A Systematic Review and Meta-analysis

BACKGROUND

Olfactory dysfunction (OD) is common and has been reported as an early indicator of COVID-19. However, the reported prevalence of OD in the general population varies widely depending upon the metric used to assess olfaction.Methodology/Principal: To perform a systematic review and meta-analysis of the prevalence of OD in the healthy general population, review the various assessment metrics used, and compare pooled OD prevalence rates.

RESULTS

A total of 175,073 subjects were identified (mean age 63.5 years, range 18 to 101) with an overall OD prevalence of 22.2% (95% CI 14.8-30.6). OD prevalence was significantly greater using objective olfactory assessments, compared to subjective measures (28.8%, CI 20.3-38.2 versus 9.5%, CI 6.1-13.5, p < 0.001). The prevalence of OD was greater using expanded identification tests (>8 items) compared to brief test with ≤8 items (30.3%, CI 16.2-46.5 versus 21.2%, CI 12.3-31.8). Prevalence was higher in studies with a mean age greater than 55 years compared to those with a mean age of 55 years or less (34.5%, CI 23.4-46.5 versus 7.5%, CI 2.6-14.5, p < 0.001).

CONCLUSIONS

The reported prevalence of OD in the general population depends on the testing method and population age. OD prevalence was greater in studies using objective tests, expanded identification tests, and in those with older subjects.

Olfactory dysfunction revisited: a reappraisal of work-related olfactory dysfunction caused by chemicals

Occupational exposure to numerous individual chemicals has been associated with olfactory dysfunction, mainly in individual case descriptions. Comprehensive epidemiological investigations into the olfactotoxic effect of working substances show that the human sense of smell may be impaired by exposure to metal compounds involving cadmium, chromium and nickel, and to formaldehyde. This conclusion is supported by the results of animal experiments. The level of evidence for a relationship between olfactory dysfunction and workplace exposure to other substances is relatively weak.

Olfactory dysfunction revisited: a reappraisal of work-related olfactory dysfunction caused by chemicals

Occupational exposure to numerous individual chemicals has been associated with olfactory dysfunction, mainly in individual case descriptions. Comprehensive epidemiological investigations into the olfactotoxic effect of working substances show that the human sense of smell may be impaired by exposure to metal compounds involving cadmium, chromium and nickel, and to formaldehyde. This conclusion is supported by the results of animal experiments. The level of evidence for a relationship between olfactory dysfunction and workplace exposure to other substances is relatively weak.

Occupational Exposure to Inhalable Manganese at German Workplaces

Due to mounting evidence of neurotoxic effects of manganese (Mn) already at low concentrations, occupational exposure limits (OELs) have been adopted. We analyzed 5771 personal measurements of inhalable manganese (Mn) together with information on sampling conditions and job tasks from the German exposure database Messdaten zur Exposition gegenüber Gefahrstoffen am Arbeitsplatz (MEGA) to assess exposure levels in welders and other occupations between 1989 and 2015. Geometric means (GMs) of exposure to Mn were estimated for various occupational settings adjusted for 2-h sampling duration and analytical method, centered at 2009. Measurements below the limit of quantification (LOQ) were multiply imputed. The median concentration was 74 µg m-3 (inter-quartile range 14-260 µg m-3) in welders and 8 µg m-3 (inter-quartile range <LOQ-31 µg m-3) in other occupations. Every third measurement was higher than 100 µg m-3, 20% exceeded 200 µg m-3, and 5% of welders inhaled concentrations ≥1000 µg m-3. GMs >100 µg m-3 were observed in gas metal and flux-cored arc welders and in shielded metal arc welders using consumables of high Mn content (>5%). Tungsten inert gas welding, laser welding and working in other occupations such as foundry worker, electroplater, or grinder were associated with GMs <10 µg m-3. A shorter sampling duration was associated with higher Mn concentrations. High-emission welding techniques require protective measures to cope with adopted OELs. Results of this study are useful to assess cumulative Mn exposure in community-based studies on neurotoxic effects.

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

Objectives

Exposure to manganese (Mn) may cause movement disorders, but less is known whether the effects persist after the termination of exposure. This study investigated the association between former exposure to Mn and fine motor deficits in elderly men from an industrial area with steel production.

Methods

Data on the occupational history and fine motor tests were obtained from the second follow-up of the prospective Heinz Nixdorf Recall Study (2011-2014). The study population included 1232 men (median age 68 years). Mn in blood (MnB) was determined in archived samples (2000-2003). The association between Mn exposure (working as welder or in other at-risk occupations, cumulative exposure to inhalable Mn, MnB) with various motor functions (errors in line tracing, steadiness, or aiming and tapping hits) was investigated with Poisson and logistic regression, adjusted for iron status and other covariates. Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated for substantially impaired dexterity (errors >90th percentile, tapping hits <10th percentile).

Results

The median of cumulative exposure to inhalable Mn was 58 µg m-3 years in 322 men who ever worked in at-risk occupations. Although we observed a partly better motor performance of exposed workers at group level, we found fewer tapping hits in men with cumulative Mn exposure >184.8 µg m-3 years (OR 2.15, 95% CI 1.17-3.94). MnB ≥ 15 µg l-1, serum ferritin ≥ 400 µg l-1, and gamma-glutamyl transferase ≥74 U l-1 were associated with a greater number of errors in line tracing.

Conclusions

We found evidence that exposure to inhalable Mn may carry a risk for dexterity deficits. Whether these deficits can be exclusively attributed to Mn remains to be elucidated, as airborne Mn is strongly correlated with iron in metal fumes, and high ferritin was also associated with errors in line tracing. Furthermore, hand training effects must be taken into account when testing for fine motor skills.

Assessment of potential predictors of calretinin and mesothelin to improve the diagnostic performance to detect malignant mesothelioma: results from a population-based cohort study

OBJECTIVES

Mesothelin and calretinin are blood-based markers for malignant mesothelioma. The objective of this study was to analyse the markers in plasma samples from cancer-free men and to identify factors influencing their concentrations to minimise false-positive test results when using these markers for the early detection of malignant mesothelioma.

SETTING

The present analyses used data and archived blood samples of the population-based Heinz Nixdorf Recall Study among elderly people collected from 2011 to 2014.

PARTICIPANTS

A total of 569 men (median age 70 years) without a malignant disease at the time of blood sampling were selected for these analyses.

PRIMARY AND SECONDARY OUTCOME

Mesothelin and calretinin concentration in plasma samples.

RESULTS

We observed 24 mesothelin concentrations ≥1.5 nM (specificity 95.8%, 95% CI 93.8% to 97.2%) and 34 calretinin concentrations ≥1.0 ng/mL (specificity 94.0%, 95% CI 91.7% to 95.7%). Only five men had both markers above these cut-offs. Renal dysfunction and hypertension were major predictors of elevated mesothelin in addition to age. Regarding calretinin, the effect of renal dysfunction was slightly weaker and hypertension was not associated with increased concentrations. However, a diagnosis of cancer after blood collection and bronchial asthma were associated with positive calretinin results.

CONCLUSIONS

The combined determination of mesothelin and calretinin results in only few false-positive marker tests. Both markers are mainly influenced by renal dysfunction. The determination of cystatin C concentrations may be informative when interpreting the test results.

Olfactory toxicity in rats following manganese chloride nasal instillation: A pilot study

Following inhalation, manganese travels along the olfactory nerve from the olfactory epithelium (OE) to the olfactory bulb (OB). Occupational exposure to inhaled manganese is associated with changes in olfactory function. This pilot study evaluated two related hypotheses: (a) intranasal manganese administration increases OE and OB manganese concentrations; and (b) intranasal manganese exposure impairs performance of previously trained rats on a go-no-go olfactory discrimination (OD) task. Male Fischer 344 rats were trained to either lever press ("go") in response to a positive conditioned stimulus (CS+: vanillin) or to do nothing ("no go") when a negative conditioned stimulus (CS-: amyl acetate) was present. Following odor training, rats were randomly assigned to either a manganese (200mM MnCl₂) or 0.9% saline treatment group (n=4-5 rats/group). Administration of either saline or manganese was performed on isoflurane-anesthetized rats as 40μL bilateral intranasal instillations. Rats were retested 48h later using the vanillin/amyl acetate OD task, then euthanized, followed by collection of the OE and OB. Manganese concentrations in tissue samples were analyzed by ICP-MS. An additional cohort of rats (n=3-4/group) was instilled similarly with saline or manganese and nasal and OB pathology assessed 48h later. Manganese-exposed rats had increased manganese levels in both the OE and OB and decreased performance in the OD task when compared with control animals. Histopathological evaluation of the caudal nasal cavity showed moderate, acute to subacute suppurative inflammation of the olfactory epithelium and submucosa of the ethmoid turbinates and mild suppurative exudate in the nasal sinuses in animals given manganese. No histologic changes were evident in the OB. The nasal instillation and OD procedures developed in this study are useful methods to assess manganese - induced olfactory deficits.

The distribution of blood concentrations of lead (Pb), cadmium (Cd), chromium (Cr) and manganese (Mn) in residents of the German Ruhr area and its potential association with occupational exposure in metal industry and/or other risk factors

OBJECTIVE

This study investigated the metal distribution in blood samples from the general population and the risk of having high metal concentration for metal workers.

METHODS

Metal concentrations were determined in archived blood samples from 1411 men and 1410 women (median age 59 and 57 years, respectively) collected at baseline (2000-2003) of the prospective Heinz Nixdorf Recall Study. Retrospective information on working in metal industry was obtained from previous follow-up survey (2011-2014). Odds ratios (ORs) with 95% confidence intervals (CI) of having a metal concentration >90th percentile (P90) for working in metal industry were calculated using logistic regression with adjustment for covariates.

RESULTS

More men than women worked in metal industry (57 vs. 3 at baseline). Male metal workers had increased blood lead (Pb) (OR: 2.86; 95% CI: 1.38-5.91) and manganese (Mn) (OR: 2.92; 95% CI: 1.46-5.81). Smoking (≥30 cigarettes/day) strongly influenced cadmium (Cd) in blood (OR: 168; 95% CI: 55-510). Women had higher Mn (8.92μg/L) and Cd (0.36μg/L) concentrations than men (Mn: 8.11μg/L; Cd: 0.29μg/L). Blood Pb in women (29.2μg/L) was lower than in men (33.2μg/L). None of the studied risk factors was significantly associated with chromium and nickel concentrations above their 90th percentiles.

CONCLUSIONS

In this population-based cohort we found evidence that working in metal industry was predictive for having elevated blood Pb and Mn concentrations. However, the 95th percentiles of all investigated metals were not significantly influenced by metal-related occupations. The present study is supportive for gender-specific reference values to limit occupational exposure to Mn and Pb. The strong influence of smoking on blood Cd hinders establishing reference values.