A Role for Air Pollution in Alzheimer's Disease

There has long been some thought that air pollution can contribute to or even cause Alzheimer's disease.  You may have read that the pandemic shutdown has led to observable decreases in the concentration of airborne pollutants, and some researchers who otherwise might have been in their laboratories have been spending time at home reviewing the topic.  And so, on May 22, the ALZForum published a two-part review which surveyed some of what we have learned.

To summarize, there is evidence of a link between air pollution and the accumulation of beta amyloid and other effects we associate with Alzheimer's disease.  For example, people living near freeways are more likely to develop Alzheimer's disease, although early studies did not control for confounding factors.  The culprits would be oxides of nitrogen and airborne particulates.

The oxides of nitrogen can enter the bloodstream through the lungs and cause damage to the cardiovascular system.  What's bad for the heart is bad for the brain, and so we have discussed previously various connections between damage to blood vessels and damage to the hippocampus and other regions of the brain.  We said this is especially a problem when the blood-brain barrier of the blood vessels is damaged, and the brain loses some protections.

Particulates, on the other hand, can enter the brain via the nose and the olfactory nerve.  This is the same pathway they used to get insulin into my brain for the SNIFF study.  You will recall from Beating the Dementia Monster that I was a study participant, although I was on the placebo.  (The study failed to find that artificially manipulating the concentration of insulin in the brain could improve cognition.)

Depending on the results of studying the effects of air pollution on mice, researchers have constructed a hypothesis by which particulates enter the brain and activate the microglia. Since the blood-brain barrier prevents the entry of antibodies into the brain, the microglia serve to attack the invading particulate bodies in their place.  But, just as with other infection, this attack involves inflammation, which gets out of control.  And inflammation plays an important role in the development of Alzheimer's disease.  There is then a cascade of events that lead to oxidative stress (so eat your blueberries!) and the accumulation of beta amyloid on the cells.  This all results in cell death and atrophy of the brain.