Magnetic Airborne Particles Linked to Development of Alzheimer’s

Tiny magnetic particles in the air could be linked to the development of Alzheimer’s disease symptoms, a new study suggests.

These particles, made of magnetite, are a relatively common air pollutant. Sources of magnetite particles include industrial combustion processes, vehicle exhaust fumes and the friction-wear of brake pads. Magnetite nanoparticles have previously been found in the human brain.

Now, a new study of mice and human neuronal cells suggests that these magnetic particles might also induce signs and symptoms of Alzheimer’s disease. The research is published in Environment International.

Investigating the causes of Alzheimer’s disease

Alzheimer's disease is a progressive, neurodegenerative disease leading to memory loss, cognitive decline and a significant reduction in a person’s overall quality of life.

While there is a genetic component to Alzheimer’s disease risk, there are many other factors that might influence whether a person develops the condition as they age.

“Fewer than 1% of Alzheimer’s cases are inherited, so it is likely that the environment and lifestyle play a key role in the development of the disease,” explained Cindy Gunawan, an associate professor at the Australian Institute for Microbiology and Infection (AIMI) and a co-first author on the new work.

One of these potential non-genetic risk factors currently being investigated by scientists like Gunawan is a person’s exposure to various toxic air pollutants.

“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,” Gunawan said. “Magnetite, a magnetic iron oxide compound, has also been found in greater amounts in the brains of people with Alzheimer’s disease.”

"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,” she added.

Exposure to magnetite induces Alzheimer’s-like behavior in mice

To examine the effects of air pollutants on the brain, the research team studied both healthy lab mice and mice that had a genetic predisposition to Alzheimer’s disease. These mice were exposed to very fine particles of iron, magnetite and diesel combustion particles over four months.

At the end of the study period, the mice that had been exposed to magnetite exhibited behaviors that were most consistent with possible Alzheimer’s disease. This included increased stress and anxiety, as well as short-term memory impairment. In the mice that were predisposed to Alzheimer’s, the memory impairment was especially pronounced.

Magnetite exposure was also associated with the loss of neuronal cells in the hippocampus and the somatosensory cortex – brain regions that are crucial to memory and bodily sensation processing, respectively. The genetically predisposed mice were also found to have an increased formation of amyloid plaque in the brain, which is a known sign of Alzheimer’s disease.

“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,” said Kristine McGrath, an associate professor at the University of Technology Sydney School of Life Sciences and the study’s senior author.

“When we inhale air pollutants, 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,” she explained.

Magnetite causes inflammation in human neuronal cells

In addition to the mice, the researchers also studied the reaction of human neuronal cells when exposed to magnetite in the lab.

They found that this exposure triggered inflammation and oxidative stress, leading to cell damage. This was also seen in the mice segment of the study. Both inflammation and oxidative stress are known contributors 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,” added co-first author Charlotte Fleming, from the University of Technology Sydney School of Life Sciences.

Based on their findings, the research team suggests that individuals should take steps to reduce their exposure to air pollution as much as possible. But they also believe these results will be of interest to health practitioners and policymakers when considering air pollution guidelines. Specifically, the researchers recommend that magnetite particles should be included in air quality index safety thresholds, as well as being considered in measures to reduce emissions from vehicles and coal-fired power stations.

Reference: Gunawan C, Fleming C, Irga PJ, et al. Neurodegenerative effects of air pollutant particles: Biological mechanisms implicated for early-onset Alzheimer’s disease. Environ Int. 2024;185:108512. doi: 10.1016/j.envint.2024.108512

This article is a rework of a press release issued by the University of Technology Sydney. Material has been edited for length and content.