Abstract：
Inhalation of welding fumes can cause metal accumulation in the brain, leading to Parkinsonian-like symptoms. Metal accumulation and altered neurochemical profiles have been observed using magnetic resonance imaging (MRI) in highly exposed welders, being associated with decreased motor function and cognition. While MRI is impractical to use as a health risk assessment tool in occupational settings, toenail metal levels are easier to assess and have been demonstrated to reflect an exposure window of 7-12 months in the past. Yet, it is unclear whether toenail metal levels are associated with brain metal levels or changes in metabolism, which are the root of potential health concerns. This study investigates whether toenail manganese (Mn) and iron (Fe) levels, assessed at several time points, correlate with brain Mn and Fe levels, measured by MRI, as well as brain GABA, glutamate (Glu), and glutathione (GSH) levels, measured by Magnetic Resonance Spectroscopy (MRS), in seventeen Mn-exposed welders. Quantitative T1 and R2* MRI maps of the whole brain, along with GABA, Glu, and GSH MRS measurements from the thalamus and cerebellum were acquired at baseline (T0). Toenail clippings were collected at T0 and every three months after the MRI for a year to account for different exposure periods being reflected by toenail clippings and MRI. Spearman correlations of toenail metal levels were run against brain metal and metabolite levels, but no significant associations were found for Mn at any timepoint. Cerebellar GSH positively correlated with toenail Fe clipped twelve months after the MRI (p = 0.05), suggesting an association with Fe exposure at the time of the MRI. Neither thalamic GABA nor Glu correlated with toenail Fe levels. In conclusion, this study cannot support toenail Mn as a proxy for brain Mn levels or metabolic changes, while toenail Fe appears linked to brain metabolic alterations, underscoring the importance of considering other metals, including Fe, in studying Mn neurotoxicity.
摘要：
吸入焊接烟雾会导致金属在大脑中积聚，导致类似帕金森病的症状.在高度暴露的焊工中使用磁共振成像（MRI）观察到金属积累和改变的神经化学特征，与运动功能和认知能力下降有关。虽然MRI在职业环境中用作健康风险评估工具是不切实际的，脚趾甲金属水平更容易评估，并已证明反映了过去7-12个月的暴露窗口。然而，目前尚不清楚脚趾甲金属水平是否与大脑金属水平或代谢变化有关，这是潜在健康问题的根源。这项研究调查了脚趾甲锰(Mn)和铁(Fe)的水平，在几个时间点评估，与大脑Mn和Fe水平相关，通过MRI测量，以及大脑GABA，谷氨酸(Glu),和谷胱甘肽（GSH）水平，通过磁共振波谱（MRS）测量，十七个锰暴露焊工。整个大脑的定量T1和R2*MRI图，和GABA一起,Glu,在基线(T0)获得来自丘脑和小脑的GSHMRS测量值。在T0和MRI后每三个月收集一次脚趾甲剪报，为期一年，以说明脚趾甲剪报和MRI反映了不同的暴露期。脚趾甲金属水平的Spearman相关性与脑金属和代谢物水平有关，但在任何时间点都没有发现Mn的显着关联。MRI术后12个月小脑GSH与趾甲Fe夹断呈正相关(p=0.05),提示与MRI时的铁暴露有关。丘脑GABA和Glu均与趾甲Fe水平无关。总之,这项研究不能支持脚趾甲Mn作为大脑Mn水平或代谢变化的替代，脚趾甲Fe似乎与大脑代谢改变有关，强调考虑其他金属的重要性，包括Fe,研究锰的神经毒性。
