'Air pollution' particles linked to Alzheimer's

Tiny metal particles from exhaust gases seem to fly up our noses and travel into our brains, where they may contribute to Alzheimer's disease, reports New Scientist.

Iron nanoparticles were already known to be present in the brain – but were previously thought to come from iron naturally found in our bodies, derived from food.

However, now after a closer look at the structures of the particles, scientists believe these mostly come from air pollution sources like traffic fumes and coal burning, reports New Scientist.

The findings are quiet conclusive, says the report quoting Barbara Maher of Lancastar University in the UK.

Iron is present in human bodies in different forms as it is part of many biological molecules. But the form known as magnetite or iron oxide has been implicated in Alzheimer's disease.

Maher's team examined the brains of 37 people living either in Manchester or in the UK or Mexico City. The study revealed millions of magnetic particles per gram of brain tissue, detected by measuring how magnetic the brain tissue was.

The surprise came when the team used electron microscopes to take a close look at particles in the front part of the brains of six people.

According to New Scientist, round particles of magnetite outnumbered angular magnetite crystals by about one hundred to one.

Crystal forms are more likely to have a natural source – such as iron that has come out of the body's cells. But round particles are generally found when iron is melted at high a temperature, exactly which happens when fuel is burned, reports New Scientist.

The shape of these particles is compelling evidence that they come from pollution. "There is iron as impurities in fuel, and there is iron in a car engine block," she says. "If you walk down the street you'll be breathing them in – how could they not get into your system?" New Scientist quoted Maher as saying.

These magnetite nanoparticles are less than 200 nanometres in diameter, so may be moving from the air into the nerve endings in our noses, and from there to the brain, Maher's team added.

The team also found that the brains contained nanoparticles of metals that are present in car engines but are rare in the body, such as platinum.

 Alzheimer's risk

Jo Anne Shatkin, at US environmental health firm Vireo Advisors, says the findings are a cause for concern. "It's not that surprising because we have known for a long time we get exposed to these nanoparticles. We are just getting a better ability to look at them."

Previous work on cells grown in the lab has suggested that iron oxide is present in the protein plaques thought to play a role in Alzheimer's disease, and that it generates reactive compounds called free radicals, which can kill nerve cells.

Population studies have found that people who live nearer busy roads have a higher risk of mental impairment in old age. But these kinds of studies have also found that our risk of getting Alzheimer's by a particular age is falling over time, so if air pollution is contributing to the disease, it doesn't seem to be making it more common.

Even so, steps to reduce air pollution might cut our risk of Alzheimer's further, says Shatkin.