Reversibility of Neuroimaging Markers Influenced by Lifetime Occupational Manganese Exposure

David A Edmondson; Ruoyun E Ma; Chien-Lin Yeh; Eric Ward; Sandy Snyder; Elham Azizi; S Elizabeth Zauber; Ellen M Wells; Ulrike Dydak

doi:10.1093/toxsci/kfz174

Reversibility of Neuroimaging Markers Influenced by Lifetime Occupational Manganese Exposure

Toxicol Sci. 2019 Nov 1;172(1):181-190. doi: 10.1093/toxsci/kfz174.

Authors

David A Edmondson^{1

2}, Ruoyun E Ma^{1

2

3}, Chien-Lin Yeh^{1

2}, Eric Ward¹, Sandy Snyder¹, Elham Azizi⁴, S Elizabeth Zauber⁵, Ellen M Wells^{1

6}, Ulrike Dydak^{1

2}

Affiliations

¹ School of Health Sciences, Purdue University, West Lafayette, Indiana 47907.
² Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, Indiana 46202.
³ Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota 55455.
⁴ Department of Neurology, Ochsner Medical Center, Kenner, Louisiana 70065.
⁵ Department of Neurology, Indiana University School of Medicine, Indianapolis, Indiana 46202.
⁶ Public Health Graduate Program, Purdue University, West Lafayette, Indiana 47907.

Abstract

Manganese (Mn) is a neurotoxicant that many workers are exposed to daily. There is limited knowledge about how changes in exposure levels impact measures in magnetic resonance imaging (MRI). We hypothesized that changes in Mn exposure would be reflected by changes in the MRI relaxation rate R1 and thalamic γ-aminobutyric acid (GABAThal). As part of a prospective cohort study, 17 welders were recruited and imaged on 2 separate occasions approximately 2 years apart. MRI relaxometry was used to assess changes of Mn accumulation in the brain. Additionally, GABA was measured using magnetic resonance spectroscopy in the thalamic and striatal regions of the brain. Air Mn exposure ([Mn]Air) and cumulative exposure indexes of Mn (Mn-CEI) for the past 3 months (Mn-CEI3M), past year (Mn-CEI12M), and lifetime (Mn-CEILife) were calculated using personal air sampling and a comprehensive work history, whereas toenails were collected for analysis of internal Mn body burden. Finally, welders' motor function was examined using the Unified Parkinson's Disease Rating Scale (UPDRS). Median exposure decreased for all exposure measures between the first and second scan. ΔGABAThal was significantly correlated with ΔMn-CEI3M (ρ = 0.66, adjusted p = .02), ΔMn-CEI12M (ρ = 0.70, adjusted p = .006), and Δ[Mn]Air (ρ = 0.77, adjusted p = .002). ΔGABAThal significantly decreased linearly with ΔMn-CEI3M (quantile regression, β = 15.22, p = .02) as well as Δ[Mn]Air (β = 1.27, p = .04). Finally, Mn-CEILife interacted with Δ[Mn]Air in the substantia nigra where higher Mn-CEILife lessened the ΔR1 per Δ[Mn]Air (F-test, p = .005). Although R1 and GABA changed with Mn exposure, UPDRS was unaffected. In conclusion, our study shows that effects from changes in Mn exposure are reflected in thalamic GABA levels and brain Mn levels, as measured by R1, in most brain regions.

Keywords: GABA; R1; magnetic resonance imaging; manganese; occupational exposure to manganese; welding.

Abstract

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