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

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 a new study in the leading journal Environmental Health Perspectives.

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 University Professor and 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 at USC.

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, Finch said.

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.

The Environmental Health Perspectives study relied on biomedical research from four USC units: the Leonard Davis School of Gerontology, the Dana and David Dornsife College of Letters, Arts and Sciences, the Keck School of Medicine and USC Viterbi.

In the study, mice were exposed for a relatively short time: 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;
• life span 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.”

The study by Finch and his colleagues adds to other evidence on the health dangers of vehicle pollution.

Research by preventive medicine faculty at the Keck School has linked proximity to freeways with increased risk of asthma and, most recently, autism (http://bit.ly/eawo4M).

Autopsies of adults in Mexico found signs of brain inflammation and premature aging in subjects from Mexico City compared to ones from the less polluted city of Veracruz (ncbi.nlm.nih.gov/pubmed/19716187).

Prior research by Sioutas found inflammatory responses in the brains of rodents exposed to freeway air, but did not study the effect of freeway particulates on brain cells (http://www.ncbi.nlm.nih.gov/pubmed/17886059).

In addition to senior author Finch, the research team consisted of lead author Todd Morgan, a research associate professor of gerontology, with fellow student David Davis and research lab technician Nahoko Iwata; neuroscientist Michel Baudry and chemist Nicos Petasis of USC College, with students Jeremy Tanner, Yu-Tien Hsu and Jeremy Winkler and David Snyder ’10; Sioutas of USC Viterbi, with students Zhi Ning and Winnie Kam; and environmental health expert Jiu-Chiuan Chen of the Keck School.

Funding came through grants from USC’s James H. Zumberge Faculty Research & Innovation Fund and the Ellison Medical Foundation.