The majority of Alzheimer's research has focused on amyloid beta (b-amyloid), but researchers have recently started to pay more attention to another protein called tau. It has been known to be associated with the disease for a while, but it hasn't been extensively studied since effective ways of imaging it were not available until now.

Researchers at Washington University School of Medicine used a new imaging agent that binds to tau protein and makes it visible on PET images, and found that measures of tau are better indicators of cognitive decline associated with Alzheimer's than amyloid beta measurements.

In the study, which was recently published in the journal, Science Translational Medicine, the researchers studied 36 control participants who were cognitively normal and 10 patients with mild Alzheimer's disease.
The lead author, Dr. Beau M. Ances, reported that the analysis helps them to establish that the new tau agent, T807, is an important tool for understanding the timeline of Alzheimer's progression and for uncovering the regions of the brain that are involved.

"It's a location, location, location kind of business," said Ances, the Associated Press reported, "The plaque starts setting up the situation, and tau is almost the executioner."

Previous studies have shown that increased levels of b-amyloid is the earliest sign of Alzheimer's, but in the earliest stages the patients are still cognitively normal. The Washington University researchers suspect that b-amyloid changes first and then tau and that it's a combination of both that causes the patient to experience mild cognitive impairment.

Besides developing a timeline, the new approach is also helpful for compiling spatial information about the affected brain regions. Increased tau in cerebrospinal fluid is a known marker of dementia, but that type of information couldn't determine which regions of the brain are gathering abnormal proteins.

Now that imaging agents for both b-amyloid and tau are available, the researchers will be able to evaluate the effectiveness of investigational therapies. The new agent for tau is approved for use in clinical trials, and the researchers believe that it will be useful for evaluating other disorders that involve excess tau buildup including traumatic brain injury.

"This is exactly the type of information we're going to need" for better treatments," said Maria Carrillo, chief science officer of the Alzheimer's Association, in the AP report. "It's cool to see the utility of this new imaging technology actually being deployed and used."

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