Brain magnetic resonance imaging and manganese concentrations in red blood cells of smelting workers: search for biomarkers of manganese exposure

Abstract

The MRI technique has been used in diagnosis of manganism in humans and non-human primates. This cross-sectional study was designed to explore whether the pallidal signal intensity in T1-weighted MRI correlated with Mn levels in the blood compartment among Mn-exposed workers and to understand to what extent the MRI signal could reflect Mn exposure. A group of 18 randomly selected male Mn-exposed workers of which 13 were smelting workers with high exposure (mean of airborne Mn in work place: 1.26 mg/m3; range: 0.31-2.93 mg/m3), and 5 power distribution control workers with low exposure (0.66 mg/m3 and 0.23-0.77 mg/m3) from a ferroalloy factory, and another group of 9 male subjects as controls from a non-smelting factory who were office or cafeteria workers (0.01 mg/m3 and 0-0.03 mg/m3) were recruited for neurological tests, MRI examination, and analysis of Mn in whole blood (MnB), plasma (MnP) or red blood cells (MnRBC). No clinical symptoms and signs of manganism were observed among these workers. MRI data showed average increases of 7.4% (p<0.05) and 16.1% (p<0.01) in pallidal index (PI) among low- and high-exposed workers, respectively, as compared to controls. Fourteen out of 18 Mn-exposed workers (78%) had intensified PI values, while this proportion was even higher (85%) among the high Mn-exposed workers. Among exposed workers, the PI values were significantly associated with MnRBC (r=0.55, p=0.02). Our data suggest that the workers exposed to airborne Mn, but without clinical symptoms, display an exposure-related, intensified MRI signal. The MRI, as well as MnRBC, may be useful in early diagnosis of Mn exposure.

Fig. 1

Representative MRI of Mn exposed workers and control workers. (A) Significantly increased T1-weighted MRI (PI = 121.5) in a smelting worker who was exposed to the high level of airborne Mn; (B) slightly increased T1-weighted MRI (PI = 112.2) in a power distribution/control worker exposed to low level of airborne Mn; and (C) normal T1-weighted MRI (PI = 102.7) in a worker without Mn exposure. (a) Coronal T1-weighted MRI, (b) axial T1-weighted MRI, and (c) axial T2-weighted MRI. Arrows indicate increased signal intensities at the globus pallidus.

Fig. 2

Scatter dot-plots of the distribution of individual MRI scores among control, low and high Mn-exposed workers. (A) Signal intensity in globus pallidus (SIGP); (B) pallidal index (PI), which is defined as the ratio of SIGP to that in the subcortical frontal white matter (SIFW) in axial T1-weighted MRI planes multiplied by 100.

Fig. 3

Correlation between MnRBC and the PI values among 18 Mn-exposed workers. Data were analyzed by linear correlation, correlation coefficient (r) = 0.55, p < 0.05.