ENZYME

Low levels of an enzyme that degrades insulin could increase the risk for Alzheimer's disease, according to a study in mice by doctors at the University of Texas Southwestern Medical Center at Dallas. The discovery targets a new correlation linking diseases like diabetes and Alzheimer's--an association that has not been understood, points out Bonnie Miller, assistant professor of internal medicine. "What's exciting is that this suggests a new mechanism that may contribute to Alzheimer's disease--the competition of multiple substrates, such as insulin and beta-amyloid, for a limiting amount of the insulysin enzyme."

The researchers studied mice that were missing insulysin gene activity. They found that the crucial enzyme, in addition to degrading insulin, does so to beta-amyloid peptides. Most importantly, even a partial decrease in insulysin activity was found to raise beta-amyloid peptide levels in the brain. High levels of the peptides increase the risk of Alzheimer's disease, which affects about 5,000,000 Americans.
"It identifies another pathway that's important in regulating levels of beta-amyloid peptide," reports Dwain Thiele, chief of hepatology. "The next step is to use this animal model to see if there is a risk for developing Alzheimer's disease."