June 25, 2007
Boxers and others who have had head injuries in their youth are at increased risk for Alzheimer's disease. So are older people who have suffered from strokes. Now, researchers have discovered new clues as to how strokes or head trauma may increase Alzheimer's risk. The findings could, one day, lead to new treatments aimed at preventing the onset of the disease.
The research team, led by Giuseppina Tesco and Rudolph Tanzi of Massachusetts General Hospital in Boston, found that during head trauma, so-called "executioner" enzymes are formed in the brain and are toxic to healthy brain cells. These enzymes can be generated by a blunt head blow or a stroke, in which blood flow and oxygen supply to the brain becomes cut off.
These enzymes also lead to increased levels of another enzyme called BACE, or beta-secretase. Beta-secretase plays an important role in the formation of plaque, which builds up in the brains of those with Alzheimer's disease. The researchers pointed out that studies have shown that "individuals with Alzheimer's disease and cerebrovascular pathologies [damage to the blood vessels in the brain caused by strokes or other injuries] show greater cognitive impairment than those exhibiting either pathology alone. These studies indicate that there is an additive or synergistic interaction between Alzheimer's disease and cerebrovascular pathologies.
"Even tiny strokes, known as 'transient ischemic attacks' and which do not cause overt symptoms like paralysis or slurred speech, can damage the brain. Over time, damage to the brain may accumulate, speeding the onset of memory loss and other Alzheimer's symptoms."
Furthermore, evidence is accumulating that stroke and transient ischemic attacks significantly increase the risk of Alzheimer's disease in elderly individual. Thus, "stroke may represent a precipitating or a triggering event in Alzheimer's disease," the authors write.
The findings offer new clues to the causes of Alzheimer's disease. Better understanding of the basic pathways that lead to the disease may one day lead to new treatments that halt, or prevent, its onset.
For more on the causes of Alzheimer's and the search for a cure, visit www.ALZinfo.org.
The findings appeared in the June 7, 2007, issue of the journal Neuron, published by Cell Press.
Tesco et al.: "Depletion of GGA3 Stabilizes BACE and Enhances b-Secretase Activity." Neuron 54, 721--737, June 7, 2007. DOI 10.1016/j.neuron.2007.05.012.