Air-pollution-derived magnetic nanoparticles found in human brains

Magnetite, a magnetic iron oxide mineral, is showing up in a place it doesn’t belong: the brain.

Researchers at the University of Lancaster found unexpectedly high levels of magnetite nanoparticles in human brain tissue they were examining with electron microscopy (Proc. Natl. Acad. Sci. USA 2016, DOI: 10.1073/pnas.1605941113). Barbara A. Maher, one of the team leaders, says that’s concerning because magnetite could be toxic to the brain, generating harmful reactive oxygen species that have been linked to Alzheimer’s disease.

Scientists first discovered magnetite particles in human brains more than two decades ago that had structures suggesting a biological origin. In contrast, the vast majority of particles found in the new study resemble magnetite from airborne pollutants.

Common sources of magnetite particles include iron impurities in burning fuel—especially diesel—and indoor sources such as printer toners, and leaky stoves.

Another recent investigation found magnetite particles in amyloid plaques, the hallmark peptide aggregates in Alzheimer’s brains (Sci. Rep. 2016, DOI: 10.1038/srep24873). But Maher and coworkers show that magnetite buildup is not necessarily linked to increasing age, as is the case for Alzheimer’s. The brain with the most magnetite was from a 32-year-old who lived in Mexico City. “His brain was absolutely, incredibly, strongly magnetic,” Maher says.

Jon Dobson, a biomedical engineer at the University of Florida who has studied magnetite in Alzheimer’s brains, says: “It is important to remember that a causal link between magnetite—or other iron compounds—and Alzheimer’s has not been unequivocally established.”