Amyloid Can Trigger Brain Damage

Article excerpt

Autopsies of Alzheimer's patients show waxy plaques of a protein called beta-amyloid littering the brain like shrapnel on a battlefield. Yet researchers have failed to establish whether beta-amyloid actually causes the disease.

Now, a study of monkeys shows that beta-amyloid can indeed damage nerve cells, or neurons, in the brain, especially in older animals.

Some researchers have suggested that an accumulation of amyloid plaques over many years contributes to Alzheimer's disease, which would help explain why the condition usually strikes the elderly. The new study, however, shows that equal amounts of beta-amyloid inserted into the brains of young and old monkeys are far more destructive in the old ones. The work appears in the July Nature Medicine.

"This animal model shows that beta-amyloid introduced into the brain at levels similar to that in Alzheimer's disease can actually cause brain cell death," says coauthor Bruce A. Yankner, a neurologist at Harvard Medical School and Children's Hospital in Boston.

The study suggests a "two-hit" pattern in Alzheimer's disease in which plaque accumulation combines with "some other age-related process that is poorly defined as of yet," says Ted M. Dawson, a neurologist at Johns Hopkins Medical Institutions in Baltimore. "It's an interesting paper."

Alzheimer's disease is the most common form of neurological impairment in the elderly, affecting about 4 million people in the United States. Short-term memory and attention often falter first, followed by language, abstract reasoning, judgment, and insight.

"I think certain protective factors [against beta-amyloid plaque] that we have as young adults gradually vanish with middle age and old age," Yankner says. These traits don't always endure into old age in the population because they would not impart any selective evolutionary advantage , he speculates.

Some Down's syndrome patients develop plaques early in life but suffer no significant neuronal loss and cognitive decline from them until middle age. …