Recovery from welding-fume-exposure-induced MRI T1 signal intensities after cessation of welding-fume exposure in brains of cynomolgus monkeys.
The shortening of the MRI T1 relaxation time, indicative of a high signal intensity in a T1-weighted MRI, is known as a useful biomarker for Mn exposure after short-term welding-fume exposure. A previous monkey experimental study found that the T1 relaxation times decreased time-dependently after exposure, and a visually detectable high signal intensity appeared after 150 days of exposure. The nadir for the shortening of the T1 relaxation time was also previously found to correspond well with the blood Mn concentration in welders, suggesting a correlation between a prolonged high blood Mn concentration and shortened T1 relaxation time. Accordingly, to clarify the clearance of the brain Mn concentration after the cessation of welding-fume exposure, cynomolgus monkeys were assigned to 3 groups-unexposed, low dose (31 mg/m(3) total suspended particulate (TSP), 0.9 mg Mn/m(3)), and high dose (62 mg/m(3) TSP, 1.95 mg Mn/m(3))-and exposed to manual metal-arc stainless steel (MMA-SS) welding fumes for 2 h per day for 8 mo in an inhalation chamber system equipped with an automatic fume generator. After reaching the peak MRI T1 signal intensity (shortest T1 relaxation time), the monkeys were allowed to recover by ceasing the welding-fume exposure. Within 2 mo, the MRI T1 signal intensities for the exposed monkeys returned to nearly the same level as those for the unexposed monkeys, indicating the potential for recovery from a high MRI T1 signal intensity induced by welding-fume exposure, even after prolonged exposure. Clearance of the Mn tissue concentration was also demonstrated in the globus pallidus, plus other tissues from the brain, liver, spleen, and blood. In contrast, there was no clearance of the lung concentrations of Mn, indicating that a soluble form of Mn was transported to the blood and brain. Therefore, the solubility of Mn in welding fumes would appear to be an important determinant as regards the retention of blood Mn levels and brain tissue Mn concentrations in welders.
Han
Jeong Hee
JH
Center for Occupational Toxicology, Occupational Safety and Health Research Institute, Korea Occupational Safety Health Agency, Daejeon, Korea.
Chung
Yong Hyun
YH
Park
Jung Duck
JD
Kim
Choong Yong
CY
Yang
Seoung Oh
SO
Khang
Hyun Soo
HS
Cheong
Hae Kwan
HK
Lee
Jong Seong
JS
Ha
Chang Soo
CS
Song
Chang-Woo
CW
Kwon
Il Hoon
IH
Sung
Jae Hyuck
JH
Heo
Jeong Doo
JD
Kim
Na-Young
NY
Huang
Mingai
M
Cho
Myung Haing
MH
Yu
Il Je
IJ
D000395:Air Pollutants, Occupational / Q000097:blood / Q000633:toxicity*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D019570:Inhalation Exposure / Q000009:adverse effects*; D008252:Macaca fascicularis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008345:Manganese / Q000097:blood / Q000633:toxicity; D013997:Time Factors; D014896:Welding / Q000379:methods*
D000395:Air Pollutants, Occupational; D008345:Manganese