Magnetic iron nanoparticles found in traffic fumes may be able to enter the brain, according to a new study that found these particles were abundant in brain tissue of 37 people.
The tiny grains may contribute to brain diseases such as Alzheimer’s disease, the researchers said.
The nanoparticles are a form of iron oxide called magnetite. In the study, published Sep. 5 in the journal Proceedings of the National Academy of Sciences, researchers found millions of magnetite particles in a gram of brain tissue.
Taking a closer look at these particles, they found striking similarities to airborne magnetite, said study author Barbara Maher, a scientist at the University of Lancaster.
“When we looked at the particles inside the brain, they were a match point for point with these magnetite particles that we see in the airborne pollution,” Maher told The Huffington Post.
Magnetite particles in the air are formed in high temperatures during combustion.
“We think what’s happening is that when you breathe these particles, they are small enough that they can travel up the nose and reach the brain through the olfactory bulb,” Maher said.
That route to the brain is one of the few that’s not protected by the blood-brain barrier, which normally restricts foreign particles in the blood from reaching the brain.
Several previous studies have suggested a link between Alzheimer’s and high levels of magnetite. The compound was thought to be naturally formed in the brain and crystallized in angular shapes.
The new study, however, found a lot of iron particles have different characteristics.
“They are rounded, matching the molten droplet shape that pollution particles generally take,” Maher said. The particles were variable in size, measuring between 10 and 150 nanometers (one-billionth of a meter) in diameter. And they occur with other foreign metal particles, such as platinum and nickel. “It’s difficult to imagine how they would be forming inside the brain.”
“The recognition that nanoparticles of industrially-generated magnetite are able to make their way into the brain tissues is disturbing,” Joseph Kirschink of CalTech, who wasn’t involved in the new study, told Newsweek. In 1992, Kirschink and his colleagues discovered that magnetite can be found inside the brain.
As an environmental scientist, Maher had been been looking at magnetic properties of air pollution in the roadside atmosphere. “It’s clear that there are abundant magnetite nanoparticles that occur as part of the urban pollution mix,” Maher said. “We use those magnetic properties to measure how much atmospheric pollution there is at different places across the city.”
She then became aware of studies suggesting that brains of people with Alzheimer’s contained more magnetite than the brains of healthy people.
A 2013 study from UCLA, for example, found higher levels of iron in the brains of 31 people with Alzheimer’s compared with 68 healthy people. For that study, the researchers focused on the hippocampus, a part of the brain involved in memory formation, which shows signs of damage early in the disease.
“The magnetite was thought to be damaging to the brain,” Maher said. “So I began to wonder about the magnetite in urban pollution. Was that able to get into the brain?”
Maher and her colleagues looked at brain tissue samples from the frontal cortex of 37 people who had lived in Mexico City and Manchester.
Among those in Manchester, the analysis showed a higher concentration of magnetite in people who were older than 65 when they died, especially those with severe to moderate Alzheimer’s.
But younger people who were exposed to high levels of air pollution in Mexico City also showed high concentrations. The highest brain magnetite content was found in a 32-year-old Mexico City resident.
Although several studies have found higher levels of iron in various brain areas of people with Alzheimer’s, it’s not fully known how iron is involved in the disease. The hallmark of Alzheimer’s disease is the accumulation of amyloid plaques between nerve cells, and a study published earlier this year found magnetite particles inside these plaques.
Maher and her team plan next to look directly at the toxicity of these magnetite particles by studying their effects on cells grown in the lab.
Another topic requiring further investigation is whether people living in suburban areas carry lower levels of the particles. This, however, will be difficult to show, because even those people could be exposed to pollution from open fires and various other sources, Maher said.
The particles are so small that wearing a mask is unlikely to be useful. To avoid getting a magnetic load from air pollution, the best option when commuting is to avoid highly polluted areas, said Maher, who tries planning her route through a park or back streets when possible.
Avoiding the curb might also be a good idea, she said. “The amount of pollution drops off rapidly farther from the curbside.”
And trees may help too. In another study, researchers showed that planting trees on the curbside considerably reduces particulates from the indoor environment of houses.