Translocation of inhaled ultrafine manganese oxide particles to the central nervous system.
BACKGROUND
Studies in monkeys with intranasally instilled gold ultrafine particles (UFPs; <100 nm) and in rats with inhaled carbon UFPs suggested that solid UFPs deposited in the nose travel along the olfactory nerve to the olfactory bulb.


METHODS
To determine if olfactory translocation occurs for other solid metal UFPs and assess potential health effects, we exposed groups of rats to manganese (Mn) oxide UFPs (30 nm; approximately 500 microg/m(superscript)3(/superscript)) with either both nostrils patent or the right nostril occluded. We analyzed Mn in lung, liver, olfactory bulb, and other brain regions, and we performed gene and protein analyses.


RESULTS
After 12 days of exposure with both nostrils patent, Mn concentrations in the olfactory bulb increased 3.5-fold, whereas lung Mn concentrations doubled; there were also increases in striatum, frontal cortex, and cerebellum. Lung lavage analysis showed no indications of lung inflammation, whereas increases in olfactory bulb tumor necrosis factor-alpha mRNA (approximately 8-fold) and protein (approximately 30-fold) were found after 11 days of exposure and, to a lesser degree, in other brain regions with increased Mn levels. Macrophage inflammatory protein-2, glial fibrillary acidic protein, and neuronal cell adhesion molecule mRNA were also increased in olfactory bulb. With the right nostril occluded for a 2-day exposure, Mn accumulated only in the left olfactory bulb. Solubilization of the Mn oxide UFPs was <1.5% per day.


CONCLUSIONS
We conclude that the olfactory neuronal pathway is efficient for translocating inhaled Mn oxide as solid UFPs to the central nervous system and that this can result in inflammatory changes. We suggest that despite differences between human and rodent olfactory systems, this pathway is relevant in humans.
Elder
Alison
A
Department of Environmental Medicine, University of Rochester, Rochester, New York 14642, USA. Alison_Elder@urmc.rochester.edu
Gelein
Robert
R
Silva
Vanessa
V
Feikert
Tessa
T
Opanashuk
Lisa
L
Carter
Janet
J
Potter
Russell
R
Maynard
Andrew
A
Ito
Yasuo
Y
Finkelstein
Jacob
J
Oberdörster
Günter
G
D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology; D002490:Central Nervous System / Q000378:metabolism*; D002712:Chlorides / Q000737:chemistry / Q000493:pharmacokinetics; D008297:Male; D017895:Manganese Compounds / Q000737:chemistry / Q000493:pharmacokinetics*; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009830:Olfactory Bulb / Q000378:metabolism; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry / Q000493:pharmacokinetics*; D012313:RNA / Q000096:biosynthesis / Q000302:isolation & purification; D051381:Rats; D011916:Rats, Inbred F344; D012995:Solubility; D014018:Tissue Distribution
D002712:Chlorides; D017895:Manganese Compounds; D009419:Nerve Tissue Proteins; D010087:Oxides; D012313:RNA; C027424:manganese oxide; C025340:manganese chloride