Nanoparticles in the brain

Nanoparticles - tiny lumps of matter that could one day to be used to build faster computer circuits and improve drug delivery systems - can travel to the brain after being inhaled, according to researchers from the United States1.

The finding sounds a cautionary note for advocates of nanotechnology, but may also lead to a fuller understanding of the health effects of the nanosized particles produced by diesel engines.

Günter Oberdörster of the University of Rochester in New York and colleagues tracked the progress of carbon particles that were only 35 nanometres in diameter and had been inhaled by rats. In the olfactory bulb - an area of the brain that deals with smell - nanoparticles were detected a day after inhalation, and levels continued to rise until the experiment ended after seven days.

"These are the first data to show this," says Ken Donaldson, a toxicologist at the University of Edinburgh, UK. "I would never have thought of looking for inhaled nanoparticles in the brain."

Substances such as drugs can cross from the brain into the blood, but Oberdörster believes that the carbon nanoparticles enter the brain by moving down the brain cells that pick up odours and transmit signals to the olfactory bulb. He says that unpublished work, in which his group blocked one of the rats' nostrils and tracked which side of the brain the nanoparticles reached, appears to confirm this.

Little is known about what effect nanoparticles will have when they reach the brain. The toxicity of the nanoparticles that are currently being used to build prototype nanosized electronic circuits - such as carbon nanotubes, which are produced in labs around the world - has not been thoroughly assessed.

But Donaldson says that there is a growing feeling that other nanoparticles, such as those produced by diesel exhausts, may be damaging to some parts of our body. He estimates that people in cities take in about 25 million nanoparticles with every breath. These particles are believed to increase respiratory and cardiac problems, probably by triggering an inflammatory reaction in the lungs.

Oberdörster's unpublished work includes evidence that some nanoparticles may trigger a similar inflammatory reaction in the brains of rats.

References
1. Oberdörster, G. et al. Translocation of inhaled ultrafine particles to the brain. Inhalation Toxicology, (in press, 2004).