Air pollution particle may induce Alzheimer's disease

Magnetite, a tiny particle found in air pollution, can induce signs and symptoms of Alzheimer’s disease. That’s according to a research team from the University of Technology Sydney (UTS), UNSW Sydney and the Agency for Science, Technology and Research (A*STAR), whose research has been published in the journal Environment International.

As noted by study co-leader Associate Professor Kristine McGrath, from the UTS School of Life Sciences, “Magnetite is a quite common air pollutant; it comes from high-temperature combustion processes like vehicle exhaust, wood fires and coal-fired power stations as well as from brake pad friction and engine wear.

“When we inhale air pollutant, these particles of magnetite can enter the brain via the lining of the nasal passage, and from the olfactory bulb, a small structure on the bottom of the brain responsible for processing smells, bypassing the blood–brain barrier.”

Previous studies have indicated that people who live in areas with high levels of air pollution are at greater risk of developing Alzheimer’s disease. Indeed, recent research out of the US found that those with higher exposure to traffic-related air pollution (in the form of fine particulate matter, or PM2.5) were more likely to have high amounts of amyloid plaques in their brains associated with Alzheimer’s after death.

“Magnetite, a magnetic iron oxide compound, has also been found in greater amounts in the brains of people with Alzheimer’s disease,” said study co-leader Associate Professor Cindy Gunawan, from the Australian Institute for Microbiology and Infection (AIMI) at UTS.

“However, this is the first study to look at whether the presence of magnetite particles in the brain can indeed lead to signs of Alzheimer’s.”

The researchers exposed healthy mice and those genetically predisposed to Alzheimer’s to very fine particles of iron, magnetite and diesel hydrocarbons over four months. Magnetite induced the most consistent Alzheimer’s disease pathologies; this included the loss of neuronal cells in the hippocampus, an area of the brain crucial for memory, and in the somatosensory cortex, which processes sensations from the body.

The researchers observed behavioural changes that were consistent with Alzheimer’s disease, including increased stress and anxiety and short-term memory impairment — the latter particularly in mice already predisposed to Alzheimer’s. Increased formation of amyloid plaque was also seen in the genetically predisposed mice.

Finally, the researchers found that magnetite induced an immune response in the mice and in human neuronal cells in the lab — it triggered inflammation and oxidative stress, which in turn led to cell damage. Inflammation and oxidative stress are significant factors known to contribute to dementia.

“The magnetite-induced neurodegeneration is also independent of the disease state, with signs of Alzheimer’s seen in the brains of healthy mice,” said Dr Charlotte Fleming, a co-first author from the UTS School of Life Sciences.

The results suggest that people should take steps to reduce their exposure to air pollution, as well as their risk of neurodegenerative disease. The study also has implications for air pollution guidelines, suggesting that magnetite particles should be included in the recommended safety threshold for air quality index. Increased measures to reduce vehicle and coal-fired power station emissions may also be needed.

Image credit: iStock.com/Werawad Ruangjaroon