Lee Eun-Young, Flynn Michael R, Du Guangwei, Lewis Mechelle M, Fry Rebecca, Herring Amy H, Van Buren Eric, Van Buren Scott, Smeester Lisa, Kong Lan, Yang Qing, Mailman Richard B, Huang Xuemei
*Department of Neurology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania.
Department of Environmental Sciences and Engineering, School of Public Health, University of North Carolina, Chapel Hill, North Carolina.
Toxicol Sci. 2015 Aug;146(2):281-9. doi: 10.1093/toxsci/kfv088. Epub 2015 May 7.
Although the essential element manganese (Mn) is neurotoxic at high doses, the effects of lower exposure are unclear. MRI T1-weighted (TIW) imaging has been used to estimate brain Mn exposure via the pallidal index (PI), defined as the T1W intensity ratio in the globus pallidus (GP) versus frontal white matter (FWM). PI may not, however, be sensitive to Mn in GP because Mn also may accumulate in FWM. This study explored: (1) whether T1 relaxation rate (R1) could quantify brain Mn accumulation more sensitively; and (2) the dose-response relationship between estimated Mn exposure and T1 relaxation rate (R1). Thirty-five active welders and 30 controls were studied. Occupational questionnaires were used to estimate hours welding in the past 90 days (HrsW) and lifetime measures of Mn exposure. T1W imaging and T1-measurement were utilized to generate PI and R1 values in brain regions of interest (ROIs). PI did not show a significant association with any measure of Mn and/or welding-related exposure. Conversely, in several ROIs, R1 showed a nonlinear relationship to HrsW, with R1 signal increasing only after a critical exposure was reached. The GP had the greatest rate of Mn accumulation. Welders with higher exposure showed significantly higher R1 compared either with controls or with welders with lower exposure. Our data are additional evidence that Mn accumulation can be assessed more sensitively by R1 than by PI. Moreover, the nonlinear relationship between welding exposure and Mn brain accumulation should be considered in future studies and policies.
尽管必需元素锰（Mn）在高剂量时具有神经毒性，但较低暴露水平的影响尚不清楚。MRI T1加权（TIW）成像已被用于通过苍白球指数（PI）估计脑锰暴露，苍白球指数定义为苍白球（GP）与额叶白质（FWM）的T1W强度比。然而，PI可能对GP中的锰不敏感，因为锰也可能在FWM中积累。本研究探讨了：（1）T1弛豫率（R1）是否能更敏感地量化脑锰积累；以及（2）估计的锰暴露与T1弛豫率（R1）之间的剂量反应关系。对35名在职焊工和30名对照者进行了研究。使用职业问卷来估计过去90天的焊接小时数（HrsW）以及锰暴露的终生测量值。利用TIW成像和T1测量来生成感兴趣脑区（ROI）的PI和R1值。PI与任何锰和/或焊接相关暴露的测量值均未显示出显著关联。相反，在几个ROI中，R1与HrsW呈非线性关系，仅在达到临界暴露后R1信号才增加。GP的锰积累率最高。与对照组或低暴露焊工相比，高暴露焊工的R1显著更高。我们的数据进一步证明，与PI相比，R1能更敏感地评估锰积累。此外，在未来的研究和政策中应考虑焊接暴露与脑锰积累之间的非线性关系。
