Bellina Veronesi

Protective mode.
A mouse microglial cell defends itself, engulfing a cluster of titanium dioxide nanoparticles (circle).

New Nano-headache?

Hundreds of tons of engineered, microscopic particles enter the environment every year, yet little is known of their biological effects. Now, a study of ultrafine particles of titanium dioxide (TiO2)--used in manufacturing, personal care and food products, and as drug carriers--indicates that even low concentrations can produce harmful "free radicals" in brain cells. The findings underscore the need to learn more about how such tiny particles interact with living tissues, the researchers say.

Previous studies have revealed that many nontoxic materials become harmful at particle sizes of less than 100 nanometers. Specifically, they can trigger the production of biologically reactive, oxygen-containing molecules such as free radicals. In addition, some types of particulate matter can enter the brain once they get into the bloodstream. Little is known about the biological effects of TiO2, but its widespread use and distribution means that humans and other animals could be widely exposed.

To investigate the biological effects of TiO2, Bellina Veronesi, a neurotoxicologist with the U.S. Environmental Protection Agency in Research Triangle Park, North Carolina, and her colleagues exposed mouse microglia--cells that protect the brain from invaders such as viruses and foreign chemicals--to a solution containing minute concentrations of TiO2. The microglia engulfed the particles and released bursts of reactive oxygen molecules for 2 hours. This didn't damage the microglia, but Veronesi says prolonged exposure to these compounds can damage neurons. In fact, a similar mechanism is thought to underlie some cardiovascular and neurodegenerative diseases, including Parkinson's and Alzheimer's, the researchers note in their report, published online 7 June in Environmental Science & Technology.

Environmental toxicologist Günter Oberdörster of the University of Rochester in New York says the research is a "good proof of principle," but without further studies it would be premature to conclude that TiO2 damages the brain. "The general message is that we should take these results seriously and be very careful with nanoparticles," he says.

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