Inhaled Nano-Size Particles Move Quickly to the Brain, Study Finds

When rats breathed in nano-size materials at a concentration routinely inhaled by factory welders, the tiny particles followed a rapid and efficient pathway from the nasal cavity to several regions of the brain, according to a study in the August issue of Environmental Health Perspectives.

The research is part of an ongoing effort by the University of Rochester Medical Center to find out if the tiniest airborne particles pose a health risk. The ultrafine manganese oxide particles used in the study are common in industrial plants, according to the study's researchers, and are the same size as nanoparticles.

Scientists also saw changes in the rats' gene expression that could signal inflammation and a cellular stress response, although they do not know yet if a buildup of ultrafine particles causes brain damage, according to lead author Alison Elder, Ph.D., research assistant professor of environmental medicine.

Nanotechnology is the manipulation of matter at the molecular level for the purpose of creating extremely small-scale (less than 100 nanometers) materials with unique properties. The manipulation of these tiny materials into bundles or rods helps in the manufacturing of smaller-than-ever electronics, optical and medical equipment. The sub-microscopic particles also are used in consumer products such as toothpaste, lotions and some sunscreens.

While nanotechnology is being hailed for its potential to yield medical and technological breakthroughs, the effects of inhaled nanoparticles on workers still is unknown.

In 2004, the Defense Department selected the University of Rochester Medical Center to lead a 5-year, $5.5 million investigation into whether the chemical characteristics of nanoparticles determine how they will interact with or cause harm to animal and human cells.

In the current study, the particles passed quickly through the rats' nostrils to the olfactory bulb, a region of the brain near the nasal cavity. They settled in the striatum, frontal cortex, cerebellum and lungs.

After 12 days, the concentration of ultrafine particles in the olfactory bulb rose 3.5-fold and doubled in the lungs, the study found.

Although the ultra-tiny particles did not cause obvious lung inflammation, several biomarkers of inflammation and stress response such as tumor necrosis factor and macrophage inflammatory protein increased significantly in the brain, according to gene and protein analyses.

"We suggest that despite differences between human and rodent olfactory systems, this pathway is likely to be operative in humans," the authors conclude.

EPA, the National Institute of Environmental Health Sciences, the Department of Defense and the Department of Energy funded the study.

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