Thursday, February 16, 2017

How is the Brain Damaged by Exposure to Traffic Related Air Pollution?

The Polluted Brain - Evidence Builds that Dirty Air Causes Alzheimer’s, Dementia (AAAS Science, Emily UnderwoodJan. 26, 2017) Also discussed here: Particulate Air Pollutants and White Matter Brain Aging (Abstract, Jiu-Chiuan Chen, Xinhui Wang, Mark A. Espeland, Helena Chui, Alzheimer’s and Dementia, Jul. 2014) And here: Traffic-related air pollution and brain development (21 page pdf, Nicholas Woodward, Caleb E. Finch and Todd E. Morgan , AIMS Environmental Science. May 6, 2015)

Today we review a series of research articles that reaffirm the health risks presented to people (and mice) who breathe in air polluted by vehicles and containing ultra-fine particles, in particular. Signs of memory loss and Alzheimer’s are evident in mice exposed to UFP. Levels of fine air particles within 50 m of major roadways are 10 times higher than at 150 m and those within 50 m stand a 12% higher risk of developing dementia. Tests involving prenatal mice showed that fetal damage can be done by fine particles without entering the placenta. The closer people live to major roadways, the smaller their celebral brain volume. What more do city planners and public health officials need to know about running highways and traffic through cities?


Key Quotes:

“Typically smaller than 0.2 µm in diameter, these “ultrafine” particles fall within a broader class of air pollutants commonly referred to as PM2.5 because of their size, 2.5 µm or less. When it comes to toxicity, size matters: The smaller the particles that cells are exposed to.. the higher their levels of oxidative stress, marked by the production of chemically reactive molecules such as peroxides, which can damage DNA and other cellular structures”

“living in places with PM2.5 exposures higher than the Environmental Protection Agency’s (EPA’s) standard of 12 µg/m3 nearly doubled dementia risk in older women. If the finding holds up in the general population, air pollution could account for roughly 21% of dementia cases worldwide”

 “Neuroimaging and neuropathological studies have found that brain aging processes predominantly affect white matter (WM) in late life. Older people living in areas with high exposures to ambient particulate matter (PM) are more likely to have cognitive declines.”

“among 6.6 million people in the province of Ontario, those living within 50 meters of a major road—where levels of fine pollutants are often 10 times higher than just 150 meters away—were 12% more likely to develop dementia than people living more than 200 meters away. “

 “In mice that breathed the dirty air, they have found, the brain’s microglia release a flood of inflammatory molecules, including tumor necrosis factor a, which is elevated in the brains of people with Alzheimer’s disease and has been linked to memory loss. The pollution-exposed mice also showed other signs of brain damage,”

 “adverse health effects of air pollution exposure increase with closeness to major road… UFP <ultra-fine particles> was reduced by approximately 80% at a distance of 150 meters from the roadway..Neither PM2.5 nor PM10 decreased substantially within 150 meters …and are decreased by less than 20% at a distance of 400 m vs. 50 m from a roadway. The rate of dilution of UFP was correlated with increased cardiopulmonary mortality, inversely with distance from roadways”

“The placenta may be more vulnerable to nanoparticle entry later in gestation, when the placental wall has thinned and is more vascularized, but also early in gestation before the placenta is fully formed …The period after the placenta is formed, but before maternal-fetal circulatory systems are fully developed, could be less vulnerable to pollution exposure, due to minimal blood flow to the fetus. Nanoparticles may even cause fetal damage without penetrating the placenta, e.g. in vitro, nanoparticles can cause DNA damage even when they do not cross a cell barrier .. We note that these are not exclusionary hypotheses, and both may potentially be occurring. “

 “Traffic related air pollution is correlated with numerous detrimental health outcomes: increased cardiovascular mortality from adulthood exposures, and low birth weight and cognitive disorders from gestational exposure. These epidemiological observations are largely verified in animal models. “

 “the closer people had lived to a major roadway—and thus the more PM2.5 they had likely been exposed to—the smaller their cerebral brain volume. The association held up even after adjusting for factors such as education, smoking, diabetes, and cardiovascular disease.”

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