Researchers looking at the brainstems of children and young adults exposed
lifelong to air pollution in Mexico City have discovered disturbing evidence
of harm.
Previous studies have linked fine particulate air pollution exposure with
Alzheimer's disease, and researchers have also reported evidence of air
pollution-derived nanoparticles in the frontal cortex of the brain.
But after examining the brainstems of 186 young Mexico City residents aged
between 11 months and 27 years of age, researchers, including Professor
Barbara Maher from Lancaster University, found markers not only of
Alzheimer's disease, but also of Parkinson's and of motor neurone disease
(MND) too. These markers of disease were coupled with the presence of tiny,
distinctive nanoparticles within the brainstem - their appearance and
composition indicating they were likely to come from vehicle pollution.
This has led researchers 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 heart and breathing rates, and how we
perceive the position and movement of our body, including, for example, our
sense of balance.
Professor Maher said: "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-, aluminium- and
titanium-rich nanoparticles in the brainstem - specifically in the
substantia nigra, and cerebellum.
"The iron-and aluminium-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).
"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."
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. 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 one thing common to all of the young people examined in the study 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
individual components - especially the mitochondria (key for generation of
energy, and signalling between cells) - and these 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. 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.
These 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.
Even in these young Mexico City residents, the type of neurological damage
associated with Alzheimer's, Parkinson's and motor neurone diseases is
already evident. These data 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.
Professor Barbara Maher said: "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 really
significant in development of neurological damage.
"With this in mind, control of nanoparticulate sources of air pollution
becomes critical and urgent."
Reference:
Calderón-Garcidueñasa L, González-Maciel A, Reynoso-Robles R, et al.
Quadruple abnormal protein aggregates in brainstem pathology and exogenous
metal-rich magnetic nanoparticles (and engineered Ti-rich nanorods). The
substantia nigrae is a very early target in young urbanites and the
gastrointestinal tract a key brainstem portal. Environ. Res. 2020;191.doi:
10.1016/j.envres.2020.110139