Sub-chronic inhalation of high concentrations of manganese sulfate induces lower airway pathology in rhesus monkeys.
BACKGROUND
Neurotoxicity and pulmonary dysfunction are well-recognized problems associated with prolonged human exposure to high concentrations of airborne manganese. Surprisingly, histological characterization of pulmonary responses induced by manganese remains incomplete. The primary objective of this study was to characterize histologic changes in the monkey respiratory tract following manganese inhalation.


METHODS
Subchronic (6 hr/day, 5 days/week) inhalation exposure of young male rhesus monkeys to manganese sulfate was performed. One cohort of monkeys (n = 4-6 animals/exposure concentration) was exposed to air or manganese sulfate at 0.06, 0.3, or 1.5 mg Mn/m3 for 65 exposure days. Another eight monkeys were exposed to manganese sulfate at 1.5 mg Mn/m3 for 65 exposure days and held for 45 or 90 days before evaluation. A second cohort (n = 4 monkeys per time point) was exposed to manganese sulfate at 1.5 mg Mn/m3 and evaluated after 15 or 33 exposure days. Evaluations included measurement of lung manganese concentrations and evaluation of respiratory histologic changes. Tissue manganese concentrations were compared for the exposure and control groups by tests for homogeneity of variance, analysis of variance, followed by Dunnett's multiple comparison. Histopathological findings were evaluated using a Pearson's Chi-Square test.


RESULTS
Animals exposed to manganese sulfate at > or = 0.3 mg Mn/m3 for 65 days had increased lung manganese concentrations. Exposure to manganese sulfate at 1.5 mg Mn/m3 for > or = 15 exposure days resulted in increased lung manganese concentrations, mild subacute bronchiolitis, alveolar duct inflammation, and proliferation of bronchus-associated lymphoid tissue. Bronchiolitis and alveolar duct inflammatory changes were absent 45 days post-exposure, suggesting that these lesions are reversible upon cessation of subchronic high-dose manganese exposure.


CONCLUSIONS
High-dose subchronic manganese sulfate inhalation is associated with increased lung manganese concentrations and small airway inflammatory changes in the absence of observable clinical signs. Subchronic exposure to manganese sulfate at exposure concentrations (< or = 0.3 mg Mn/m3) similar to the current 8-hr occupational threshold limit value established for inhaled manganese was not associated with pulmonary pathology.
Dorman
David C
DC
CIIT Centers for Health Research, P.O. Box 12137, Research Triangle Park, NC 27709-2137, USA. dorman@ciit.org
Struve
Melanie F
MF
Gross
Elizabeth A
EA
Wong
Brian A
BA
Howroyd
Paul C
PC
D000208:Acute Disease; D000280:Administration, Inhalation; D000336:Aerosols / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000633:toxicity; D000393:Air Pollutants / Q000493:pharmacokinetics / Q000633:toxicity*; D000818:Animals; D002908:Chronic Disease; D004305:Dose-Response Relationship, Drug; D008168:Lung / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology*; D008253:Macaca mulatta; D008297:Male; D017895:Manganese Compounds / Q000493:pharmacokinetics; D011014:Pneumonia / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology*; D013431:Sulfates / Q000493:pharmacokinetics / Q000633:toxicity*
D000336:Aerosols; D000393:Air Pollutants; D017895:Manganese Compounds; D013431:Sulfates; C039798:manganese sulfate