A new study from Lancaster University researchers reports on the presence of magnetic nanoparticles in the human brain, possibly stemming from air pollution. The ability of these particles to create reactive oxygen species – also referred to as free radicals – in mammalian cells, in combination with links between these radicals and diseases such as Alzheimer's and Parkinson's, is prompting scientists to consider the possibility that some air could be a contributor to neurodegenerative diseases.

In the past 20 years, research has shown that magnetite – a mineral previously known to be biochemically formed by various living organisms including bacteria – is present in the human brain. Although scientists believe that it likely originates from the iron present in normally-functioning brains, these nanoparticles are nevertheless toxic due to their highly magnetic nature, which causes oxidative stress and creates a favorable environment for the creation of free radicals.

"Magnetite contains both ferric (oxidized) iron and ferrous (reduced) iron; the ferrous iron can catalyze the formation of reactive oxygen species because it is redox active," Barbara Maher of Lancaster University and lead author of the study told New Atlas.

When observed naturally in the brain, magnetite nanoparticles are angular in shape. However, when these particles are created through high-temperature processes – such as those produced by vehicle engines or brake pads – their shape is circular.

In the current study, Maher and her team used spectroscopic analysis to identify magnetite nanoparticles in brain tissue derived from 37 individuals between the ages of three and 92 years old from Mexico City and Manchester. Interestingly, many of the observed particles were spherical and possessed characteristics indicative of high-temperature formation.

"The particles we found are strikingly similar to the magnetite nanospheres that are abundant in the airborne pollution found in urban settings, especially next to busy roads, and which are formed by combustion or frictional heating from vehicle engines or brakes," says Maher.

The spherical magnetite observed in the study possessed diameters of up to 150 nanometers, which fits with an inhalation model as particles smaller than 200 nanometers are small enough to make their way into the human brain through the olfactory nerve after being breathed in through the nose.

"This finding opens up a whole new avenue for research into a possible environmental risk factor for a range of different brain diseases," adds David Allsop, also of Lancaster University and co-author of the study.

Now that this study has shown that magnetite particles originating from air pollution exist in the human brain, future research can focus on determining if their presence is indeed linked to diseases such as Alzheimer's, Parkinson's and possibly some brain cancers. Indeed, previous research suggests that magnetite increases the toxicity of beta amyloid plaques, one of the protein clumps involved in Alzheimer's disease, and points to a connection between higher levels of magnetite in the brains of those with Alzheimer's disease.

The findings were published in the Proceedings of the National Academy of Sciences.

The following video further explains the findings.