Freeway air may speed up Alzheimer’s

USC (US) — If mice had to commute, exposure to vehicle pollution could make it progressively harder to navigate the maze of Los Angeles freeways.

A new study reveals that a mix of tiny particles from burning fossil fuel and weathering of car parts and pavement significantly damages the brains of mice, a finding that is relevant to memory loss and Alzheimer’s disease in humans.

Details are published in the journal Environmental Health Perspectives.

For the study, the first to explore the physical effect of freeway pollution on brain cells, researchers recreated air laden with freeway particulate matter inside the laboratory and found that whether in a test tube or in live mice, neurons involved in learning and memory showed significant damage and did not grow as well. After exposure, the brain also shows signs of inflammation associated with premature aging and Alzheimer’s disease.

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,” says Caleb Finch, professor of gerontology and biological science at University of Southern California.

Co-author Constantinos Sioutas, professor of civil and environmental engineering,  developed the technology for collecting freeway particulates in a liquid suspension and recreating polluted air in the laboratory, making it possible to conduct a controlled study on cultured brain cells and live animals.

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 says.

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

  • Memory functions in animals exposed to freeway particulates and the effects of development of mice exposed prenatally, including lifespan.
  • 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 and the chemical interactions between freeway particles and brain cells.

If further studies confirm that freeway particulates pose a human health hazard, solutions will be hard to find, Finch says. Even an all-electric car culture would not solve the problem on its own.

“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 colleagues adds to other evidence on the health dangers of vehicle pollution. Previous research has linked proximity to freeways with increased risk of asthma and, most recently, autism.

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 (study here).

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

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