xray image of human head with cloud inside to illustrate the effect of air pollution on the brain
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Researchers from various academic institutes in China and the University of Birmingham in the U.K. discovered fine particles from air pollution in the cerebrospinal fluid of patients with brain diseases, providing new evidence to support a link between air pollution and poor brain health.

The research team investigated how the particles could reach the brain in cell lines in the lab and in a mouse model, showing the likely route is via the lungs and then the blood stream. They also showed that the fine particles took a long time to clear from the brain compared with other organs in the mouse model, which suggests possible long-term effects on the brain.

Air pollution continues to worsen, particularly in big cities. Previous research has suggested that the lungs and cardiovascular system are the most likely casualties of extended exposure to air pollution, but more recent evidence suggests the brain is also impacted.

For example, exposure to contaminated air likely speeds brain aging, increasing the risk of dementia and reduced cognitive function, as well as increasing the prevalence of mental illnesses such as depression and schizophrenia and increasing the likelihood of stroke.

In this study, published in the journal PNAS, the researchers assessed whether fine air pollution particles were present in cerebrospinal fluid from 25 patients with brain disease who had not previously undergone brain surgery. Overall, fine particles were found in 8 (32%) of the patients including previously identified air pollution particles containing calcium, silicon and iron, and some more unusual particles containing compounds such as malayaite, a pigment used in the ceramics industry. For comparison purposes, these samples were compared with 26 taken from healthy controls, only one of which contained fine air pollution particles.

Through further study in the lab, the team showed that these particles enter the blood stream through the lungs and then some are able to cross the blood–brain barrier and enter the brain.

“In the lung to brain route, particles must circulate through the bloodstream, and they likely acquire a layer of absorbed proteins and other biomolecules, which is referred to as corona formation…and may cross from the bloodstream through the blood–brain barrier without visibly damaging it for final localization in the ventricles of the brain,” explain the authors.

In a mouse model, the researchers also observed that when they reached the brain the particles were hard for the body to clear.

“This work sheds new light on the link between inhaling particles and how they subsequently move around the body,” commented study author Iseult Lynch, a professor at the University of Birmingham, in a press statement.

“The data suggests that up to eight times the number of fine particles may reach the brain by travelling, via the bloodstream, from the lungs than pass directly via the nose—adding new evidence on the relationship between air pollution and detrimental effects of such particles on the brain.”

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