Air pollution in urban environments has long been associated with poor health. Breast cancer, immune dysfunction, osteoporosis, heart problems and dementia have all been linked to air pollution, however, understanding exactly how poor air quality is explicitly causing disease has been a challenge for researchers.
Epidemiological links between Alzheimer’s and air pollution have long been detected. We know people who live in particularly polluted urban areas tend to report slightly higher rates of neurodegenerative disease.
Cindy Gunawan, lead researcher on a new study looking at the mechanisms behind air pollution’s link with neurodegeneration, says most cases of late-stage Alzheimer’s disease are strongly influenced by environmental or lifestyle factors. And one particular element in air pollution is of great interest to Gunawan.
“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.”
For several decades we have known that magnetite particles can emerge naturally in a human brain. It was thought these tiny magnetic particles were a natural byproduct of the way a brain processes iron.
But in 2016, a landmark study presented a stark new hypothesis. That research closely examined brain tissue samples from 37 deceased individuals. It found plenty of magnetite particles in frontal cortex tissue, and the majority seemed to be derived from pollution. According to the 2016 study, endogenously-formed magnetite take a completely different shape to particles that come from air pollution – and these air pollution particles outnumber naturally derived particles in most human brains by 100 to one.
A working hypothesis emerged to suggest it could be magnetite in air pollution that is particularly increasing a person’s risk for Alzheimer’s.
“Magnetite is a quite common air pollutant,” explained Kristine McGrath, a co-author on the new study from the University of Technology Sydney. “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.”
Using mice engineered to be susceptible to Alzheimer's disease, the researchers looked at the effects of sustained exposure to magnetite air pollution, as well as iron and diesel pollution. While none of the pollution exposures led to good outcomes in the animals, the researchers found magnetite specifically, “increased anxiety and stress, neuronal cell loss, as well as inflammation and oxidative stress." All key pathological signs of Alzheimer's disease.
Ultimately the findings are another piece of evidence affirming air pollution is likely harmful to our brain. And the researchers do suggest magnetite levels be incorporated into new air quality safety standards. However, for most of us, we can still consider poor urban air to be a single, harmful homogenous entity. It may be magnetite causing the most damage in terms of neurodegenerative disease, but all these problematic pollutants come from the same sources – vehicle emissions and emissions from coal-fired power stations.
The new research was published in Environment International.
Source: University of Technology Sydney
