Can air pollution cause Alzheimer's, Parkinson's? Study links nanoparticles in young brains to these diseases
Air pollution particles found in brains of children and young adults have now being linked to Alzheimer's and Parkinson's disease. Researchers who looked at the brainstems of children and young adults exposed lifelong to air pollution saw disturbing evidence of harm: they found markers of Alzheimer's disease, Parkinson's and Motor Neuron Disease (MND).
These markers of disease were coupled with the presence of tiny, distinctive nanoparticles within the brainstem, and their appearance and composition suggested that they were likely to come from vehicle pollution. This has led the team to conclude that air pollution of this nature, whether inhaled or swallowed, puts people at risk of potential neurological harm.
The brainstem is the posterior part of the brain which regulates the central nervous system, controls the heart and breathing rates, and how people perceive the position and movement of the body, including, for example, their sense of balance. The new findings show that pollution-derived, metal-rich nanoparticles can reach the brainstem whether by inhalation or swallowing and that they are associated with damage to key components of nerve cells in the brainstem, "including the substantia nigra."
"Not only did the brainstems of the young people in the study show the 'neuropathological hallmarks' of Alzheimer's, Parkinson's and MND, they also had high concentrations of iron-rich, aluminum-rich and titanium-rich nanoparticles in the brainstem, specifically in the substantia nigra and cerebellum. The iron-and aluminum-rich nanoparticles found in the brainstem are strikingly similar to those which occur as combustion and friction-derived particles in air pollution (from engines and braking systems)," writes study author Professor Barbara Maher from Lancaster University in the analysis published in Environmental Research.
She adds, "The titanium-rich particles in the brain were different, distinctively needle-like in shape. Similar particles were observed in the nerve cells of the gut wall, suggesting these particles reach the brain after being swallowed and moving from the gut into the nerve cells which connect the brainstem with the digestive system."
A common aspect among all young people examined was their exposure to high levels of particulate air pollution. Professor Maher says that the associations between the presence of damage to cells and their components — especially the mitochondria, which is key for generation of energy, and signaling between cells — and the metal-rich nanoparticles are a "smoking gun".
Such metal-rich particles can cause inflammation and also act as catalysts for excess formation of reactive oxygen species, which are known to cause oxidative stress and eventual death of neurons, explains the team.
In the current study, the authors examined the brainstems of 186 young residents of Mexico City, aged between 11 months and 27 years of age. They found evidence of Alzheimer's, Parkinson's and MND in the brains of young people exposed to dirty air. According to the analysis, the "neuropathological hallmarks" found even in the youngest infant (11 months old) included nerve cell growths and plaques and tangles formed by misfolded proteins in the brain.
"Even in the young Mexico City residents, the type of neurological damage associated with Alzheimer's, Parkinson's and Motor Neuron Diseases is already evident. Damage to the substantia nigra is directly linked with the development of Parkinson's disease in later life. Protein misfolding linked previously with MND was also evident, suggesting common causal mechanisms and pathways of formation, aggregation and propagation of these abnormal proteins," the findings state.
It adds: "Critically, the brainstems of age and gender-matched controls who lived in lower-pollution areas have not shown the neurodegenerative pathology seen in the young Mexico City residents."
The investigators warn that the findings indicate the potential for a "pandemic of neurological disease in high-pollution cities around the world" as people experience longer lifespans, and full symptoms of earlier, chronic neurological damage develop.
"It's critical to understand the links between the nanoparticles you're breathing in or swallowing and the impacts those metal-rich particles are then having on the different areas of your brain. Different people will have different levels of vulnerability to such particulate exposure but our new findings indicate that what air pollutants you are exposed to, what you are inhaling and swallowing, are significant in the development of neurological damage. With this in mind, control of nanoparticulate sources of air pollution becomes critical and urgent,” Professor Barbara Maher concludes.
Commenting on the report, Dr Susan Kohlhaas, director of research from Alzheimer’s Research, UK, explains, that air pollution is linked to many adverse health conditions and a growing body of evidence suggests this includes our risk of developing dementia.
"Proteins do build up in the brain years before we see visible dementia symptoms, but more research is needed before we can suggest air pollution drives brain changes associated with disease in children. Importantly, this study provides no evidence that the changes in these brains caused dementia in these individuals, most of whom died of unrelated causes before they went on to develop the condition," she says.