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Tiny Inhaled Particles Take Easy Route from Nose to Brain

Thursday, August 3, 2006

When rats breathed in nano-sized 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 this study are common in industrial plants, and are the same size as nanoparticles, which are controversial due to concerns about their safety.

Scientists also saw changes in the rats’ gene expression that could signal inflammation and a cellular stress response, but they do not know yet if a buildup of ultrafine particles causes brain damage, said lead author Alison Elder, Ph.D., research assistant professor of Environmental Medicine.

Nanotechnology is fast-growing new wave of science that deals with nanoparticles engineered from many materials such as carbon, zinc and gold, which are less than 100 nanometers in diameter. 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 are also used in consumer products such as toothpaste, lotions and some sunscreens.

Some doctors and scientists are concerned about what happens at the cellular level after exposure to the ultrafine or nano-sized particles, and the University of Rochester is at the forefront of this type of environmental health research. In 2004 the Defense Department selected the Medical Center to lead a five-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.

The U.S. Environmental Protection Agency, National Institute of Environmental Health Sciences, Department of Defense and Department of Energy funded the study.

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