Abstract |
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.
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Authors | Jeong Hee Han, Yong Hyun Chung, Jung Duck Park, Choong Yong Kim, Seoung Oh Yang, Hyun Soo Khang, Hae Kwan Cheong, Jong Seong Lee, Chang Soo Ha, Chang-Woo Song, Il Hoon Kwon, Jae Hyuck Sung, Jeong Doo Heo, Na-Young Kim, Mingai Huang, Myung Haing Cho, Il Je Yu |
Journal | Inhalation toxicology
(Inhal Toxicol)
Vol. 20
Issue 12
Pg. 1075-83
(Sep 2008)
ISSN: 1091-7691 [Electronic] England |
PMID | 18728992
(Publication Type: Comparative Study, Journal Article)
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Chemical References |
- Air Pollutants, Occupational
- Manganese
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Topics |
- Air Pollutants, Occupational
(blood, toxicity)
- Animals
- Brain
(drug effects, metabolism)
- Inhalation Exposure
(adverse effects)
- Macaca fascicularis
- Magnetic Resonance Imaging
(methods)
- Male
- Manganese
(blood, toxicity)
- Time Factors
- Welding
(methods)
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