Study explores physical effect of freeway pollution on brain cells

University of Southern CaliforniaApr 7 2011

If mice commuted, their brains might find it progressively harder to navigate the maze of Los Angeles freeways.

A new study reveals that after short-term exposure to vehicle pollution, mice showed significant brain damage - including signs associated with memory loss and Alzheimer's disease.

The mind-numbing toxin is not an exhaust gas, but a mix of tiny particles from burning of fossil fuel and weathering of car parts and pavement, according to the study to be published Thursday, April 7 in the leading journal Environmental Health Perspectives.

Many studies have drawn a link between vehicle pollution and health problems. This is the first to explore the physical effect of freeway pollution on brain cells.

The authors found a way to recreate air laden with freeway particulate matter inside the laboratory. Whether in a test tube or in live mice, brain cells showed similar responses:

• Neurons involved in learning and memory showed significant damage,
• The brain showed signs of inflammation associated with premature aging and Alzheimer's disease,
• Neurons from developing mice did not grow as well.

The freeway particles measured between a few dozen to 200 nanometers - roughly one-thousandth the width of a human hair, and too small for car filtration systems to trap.

"You can't see them, but they are inhaled and have an effect on brain neurons that raises the possibility of long-term brain health consequences of freeway air," said senior author Caleb Finch, an expert in the effects of inflammation and holder of the ARCO/William F. Kieschnick Chair in the Neurobiology of Aging.

Co-author Constantinos Sioutas, of the USC Viterbi School of Engineering, developed the unique technology for collecting freeway particulates in a liquid suspension and recreating polluted air in the laboratory. This made it possible to conduct a controlled study on cultured brain cells and live animals. (For all co-authors and access to the study after the embargo lifts: http://ehponline.org/article/info:doi/10.1289/ehp.1002973)

Exposure lasted a total of 150 hours, spread over 10 weeks, in three sessions per week lasting five hours each.

"Of course this leads to the question, 'How can we protect urban dwellers from this type of toxicity?' And that's a huge unknown," Finch said.

The authors hope to conduct follow-up studies on issues such as:

• Memory functions in animals exposed to freeway particulates,
• Effects on development of mice exposed prenatally,
• Lifespan of exposed animals,
• Interaction of particulates with other components of smog, such as heat and ozone,
• Potential for recovery between periods of exposure,
• Comparison of effects from artificially and naturally occurring nanoparticles,
• Chemical interactions between freeway particulates and brain cells.

If further studies confirm that freeway particulates pose a human health hazard, solutions will be hard to find.

Even an all-electric car culture would not solve the problem on its own, Finch said.

"It would certainly sharply decrease the local concentration of nanoparticles, but then at present electrical generation still depends upon other combustion processes - coal - that in a larger environment contribute nanoparticles anyway.

"It's a long-term global project to reduce the amount of nanoparticles around the world. Whether we clean up our cars, we still have to clean up our power generation."