Air pollution, the pervasive yet often overlooked menace, has been observed to negatively impact the prognosis of ischemic stroke, a condition caused by reduced blood flow to the brain.
However, the specific mechanism that drives this detrimental effect has long eluded scientists.
A team of researchers recently embarked on a mission to unravel this mystery, focusing on neuroinflammation, or inflammation of the brain, as the potential main culprit.
Their groundbreaking findings were published in the February 16, 2023, issue of Particle and Fibre Toxicology.
The Experiment: Investigating the Effects of Urban Aerosols
The team exposed mice to urban aerosols from Beijing, China, via the nose for a week, and compared them to a control group of mice that were not subjected to air pollution.
The researchers found that the mice exposed to the urban aerosols exhibited increased neuroinflammation and worsening movement disorders after experiencing an ischemic stroke.
This finding suggested a direct link between air pollution and the exacerbation of stroke symptoms.
Interestingly, the researchers did not observe this effect in mice lacking a receptor for polycyclic aromatic hydrocarbons (PAHs), chemicals released by the burning of fossil fuels, wood, garbage, and tobacco.
This finding hinted at the involvement of PAHs in the heightened neuroinflammation and increased movement disorders associated with air pollution exposure in ischemic stroke.
A Closer Look: Identifying Specific Components of Air Pollution
Having established a connection between air pollution and the progression of ischemic stroke, the research team went a step further.
They aimed to identify specific components of air pollution that could be directly contributing to the poorer prognoses in ischemic stroke.
In the study, they found that exposing mice to air pollution from Beijing led to increased neuroinflammation after ischemic stroke through the activation of microglial cells, the immune cells of the brain.
This exposure also negatively affected movement disorder in the mice after the stroke.
In a second set of experiments, the team replaced Beijing’s air pollution with PM2.5 (tiny aerosolized particles of air pollution that are 2.5 micrometers in width or less) from Yokohama, Japan.
Similar results were observed, suggesting that the PM2.5 fraction of urban air pollution contains the chemicals responsible for increased neuroinflammation and the deterioration of ischemic stroke prognosis.
Role of PAHs: Linking Air Pollution to Stroke Prognosis
To identify the specific chemicals in air pollution contributing to the decreased ischemic stroke prognosis, the team used mice lacking the aryl hydrocarbon receptor, a receptor activated by the presence of PAHs.
They found that these mice showed lower microglial cell activation and movement disorder compared to normal mice.
This discovery suggests that PAHs present in Beijing’s air pollution could be partly responsible for the neuroinflammation and poorer prognosis observed in ischemic stroke mice exposed to air pollution.
The Next Steps: Seeking Better Understanding
The research team’s ultimate goal is to understand better how PM2.5 causes neuroinflammation.
Since air pollution is first inhaled into the respiratory tract, the team is now grappling with questions like: “Can small particles move from the nose to the brain?
Does lung or systemic inflammation affect the brain immune system?” These questions will guide the next stages of their research, as they continue to explore the complex impact of air pollution on stroke prognosis.
If you care about stroke, please read studies about a breakfast linked to better blood vessel health, and olive oil could help lower risks of heart disease and stroke.
For more information about health, please see recent studies about how Mediterranean diet could protect your brain health, and wild blueberries can benefit your heart and brain.
The study was published in Particle and Fibre Toxicology.
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