Welding-related brain and functional changes in welders with chronic and low-level exposure

• Published in: Neurotoxicology (Park Forest South) 2018-01, Vol.64, p.50-59
• Main Authors: Lee, Eun-Young, Flynn, Michael R., Lewis, Mechelle M., Mailman, Richard B., Huang, Xuemei
• Format: Article
• Language: English
• Subjects: Accumulation; Adult; Basal ganglia; Brain; Brain - pathology; Brain - physiopathology; Exposure; Fractional anisotropy; Ganglia; Globus pallidus; Human exposure; Humans; Iron; Iron - metabolism; Levels; Magnetic resonance imaging; Male; Manganese; Manganese - metabolism; Manganese Poisoning - complications; Manganese Poisoning - pathology; Manganese Poisoning - physiopathology; Middle Aged; Motor Disorders - chemically induced; Neurotoxicity; NMR; Nuclear magnetic resonance; Occupational Exposure; Pallidal index; Public health; Substantia alba; Synergy; Welders; Welding; Welding machines
• ISSN: 0161-813X; 1872-9711
• DOI: 10.1016/j.neuro.2017.06.011

•Manganese (Mn) may accumulate in the brain in a non-linear fashion: MRI R1 signals increased only after a critical level of exposure was reached.•Chronic Mn-exposure may lead to microstructural changes as indicated by lower DTI fractional anisotropy values in the basal ganglia.•Mn-related subtle motor dysfunctions can be captured by synergy metrics (indices for motor stability).•Iron may also play a role in welding-related neurotoxicity, especially at low-level Mn-exposure. Although an essential nutrient, manganese (Mn) can be toxic at high doses. There is, however, uncertainty regarding the effects of chronic low-level Mn-exposure. This review provides an overview of Mn-related brain and functional changes based on studies of a cohort of asymptomatic welders who had lower Mn-exposure than in most previous work. In welders with low-level Mn-exposure, we found: 1) Mn may accumulate in the brain in a non-linear fashion: MRI R1 (1/T1) signals significantly increased only after a critical level of exposure was reached (e.g., ≥300 welding hours in the past 90days prior to MRI). Moreover, R1 may be a more sensitive marker to capture short-term dynamic changes in Mn accumulation than the pallidal index [T1-weighted intensity ratio of the globus pallidus vs. frontal white matter], a traditional marker for Mn accumulation; 2) Chronic Mn-exposure may lead to microstructural changes as indicated by lower diffusion tensor fractional anisotropy values in the basal ganglia (BG), especially when welding years exceeded more than 30 years; 3) Mn-related subtle motor dysfunctions can be captured sensitively by synergy metrics (indices for movement stability), whereas traditional fine motor tasks failed to detect any significant differences; and 4) Iron (Fe) also may play a role in welding-related neurotoxicity, especially at low-level Mn-exposure, evidenced by higher R2* values (an estimate for brain Fe accumulation) in the BG. Moreover, higher R2* values were associated with lower phonemic fluency performance. These findings may guide future studies and the development of occupation- and public health-related polices involving Mn-exposure.