Patient Summary

Background
Patients with Alzheimer disease (AD) have elevated levels of a small protein called amyloid-β peptide that sticks together to form what are known as amyloid plaques in their brains. This peptide is normally made at low levels in healthy individuals, and is made when a larger protein called amyloid precursor protein (APP) is cut down in size. New treatments are now being developed that will decrease the amount of Aβ produced from APP. However, it is not clear whether lowering the production of Aβ will allow the brain to heal itself by clearing the amyloid plaques. The answer to this question may be important for deciding when Aβ-lowering drugs should be started, and may also determine how effective they are in reversing the mental symptoms of AD.

What Did the Researchers Do and Find?
Because new drugs designed to lower Aβ levels are still in development, they are not available for testing in animal models of the disease. Instead, basic questions about the effectiveness of this type of treatment must be answered using systems that mimic how the drugs work. To do this, the authors created mice that produce too much APP and that develop the same amyloid lesions as do human patients with AD. Unlike normal mice, these mice also carried a “switch” gene that allowed the researchers to turn off APP by feeding the mice special food. Turning off APP in these mice had the same effect as treating them with Aβ-lowering drugs, and so the researchers were able to ask what happened to the amyloid plaques after Aβ production was shut down. They showed that lowering Aβ production prevents the amyloid lesions from getting worse as the disease progresses. This means that treatment with Aβ-lowering drugs may be able to stop the disease from filling the brain with plaques. However, the researchers also found that the amyloid lesions that had formed before treatment was started remained intact throughout the experiment.

What Do These Findings Mean?
These results indicate that treatments designed to lower the production of Aβ may be an important part of future AD treatment, as this approach seems to prevents additional amyloid plaques from forming in the mouse brain. However, by itself, this strategy may not be able to rid the brain of plaques that have already formed in the brain before treatment is started. The findings suggest that early treatment may be important for this approach to succeed.

Where Can I Get More Information Online?
MedlinePlus has several Web pages of information on Alzheimer disease:
http://www.nlm.nih.gov/medlineplus/alzheimersdisease.html
The ADEAR Center of the US Government's National Institute on Aging also has information on Alzheimer disease:
http://www.alzheimers.org/
The Alzheimer's Association Web site contains information on both caregiving and research:
http://www.alz.org