Inflammation in the body has gotten a bad rap recently, thanks to the exacerbating role it may play in health problems such as heart disease and cancer. Now there may be one more malady to add to the list: Alzheimer’s disease.
When inflammation arises in the body as a result of infection or injury, the immune response also appears to accelerate memory loss in people with Alzheimer’s, according to a recent study published in the journal Neurology. In this study of changes in patients’ cognitive abilities over a span of six months, Alzheimer’s patients who had chronic (ongoing) inflammation as a result of, for instance, obesity or arthritis experienced four times the amount of memory loss as compared with patients without such inflammation. And those with chronic inflammation who also experienced an acute immune response (short-term, such as from an infection) were even worse off: their memory loss accelerated 10 times faster than patients without any inflammation.
“When we started the study, we thought short-lived events would be important,” says lead author Clive Holmes, a professor of biological psychiatry at the University of Southampton in England. “We hadn’t realized how important chronic inflammation was going to be.”
So how does inflammation, whether from an infection or from chronic disease, damage the brain? The answer lies in the body’s immune response, which launches an attack on invading pathogens, releasing inflaming proteins such as tumor necrosis factor, or TNF. This molecule causes the vagus nerve, which extends from the brain to the abdomen and controls vital functions such as heartbeat, to send an electrical impulse to the brain, thereby directing the brain to secrete its own immune messengers.
In people with healthy brains, this chain of events merely leads us to feel under the weather for a few days. But cells in the brains of Alzheimer’s patients may be in a constant state of low-level inflammation. Therefore, if they are exposed to a pathogenic threat or chronic disease, they can leap into full-fledged inflammation, releasing compounds that ultimately kill brain cells. Scientists aren’t quite sure why cells end up dying, but some neurons may be annihilated in an effort to stop the virus’s spread, whereas others could be destroyed by accident in the quest to rid the body of invaders, Holmes says.
The study’s results could help physicians minimize Alzheimer’s memory loss by cutting chronic inflammation, such as by helping their patients lose excess weight. Or researchers could try to aim right at the source: “If inflammation in the body is causing [inflammation] in the brain and if you can dampen that signal, blocking TNF could play a role in slowing Alzheimer’s disease,” Holmes states.
Note: This story was originally printed with the title "Inflamed Neurons"