Science News - September 10, 2011

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going in two opposite directions,” says
study coauthor and psychiatrist Yvette
Sheline, also of Washington University.
“We think depression pushes you toward
dementia, but antidepressant treatment
pushes you toward protection.”
Finding similar results in mice and
humans lends the study credibility,
Weiner says. “When you have animal data
and human data coming together, then
you start to get really excited,” he says.

Still, Weiner and others caution that it would be premature to conclude that antidepressants protect against A-beta buildup or that fewer plaques necessarily translate into less disease.

The study uncovered an association — not a clear-cut cause and effect, Weiner notes. “We cannot say with certainty that the reason why people who took the SSRIs have lower cortical amyloid is due to the fact that they took SSRIs,” he says.

And molecular neuroscientist Heather Snyder of the Alzheimer’s Association in Chicago points out that even if antidepressants are shown to reduce A-beta, scientists still don’t know how A-beta levels affect the brain. “We don’t

Researchers used a chemical called PIB to compare the amount of plaque in the brains of people who hadn’t taken antidepressants with the amount in the brains of those who had. The images above show the PIB signal difference (red represents the most difference, blue the least) between the groups in horizontal slices, starting at eye level (left) and moving up to the top of the brain (right).

really know what modulating amyloid
will do to cognition,” she says. “And we
don’t know if we need to reduce it by
10 percent or 20 percent, or if it needs to
be completely reversed.”
Another confounding factor is that
A-beta can take several forms in the
brain, from small molecules to large,
sticky clumps, and some forms may be
more dangerous than others. Interpret-
ing the A-beta clumps that PIB detects in
human brain scans remains challenging.

“We’re being very cautious,” Cirrito
says. “There are a lot of people on these
drugs, and we don’t want to get anybody
overly excited without reason.” He and
his colleagues plan to test whether acute
doses of SSRIs change A-beta levels
in the cerebrospinal fluid of healthy
human subjects.

Back Story | ALZHEIMER’S ON THE RISE Change in number of deaths (U.S.) between 2000 and 2008

-3%

-8%

-13%

-20%

though the link between Alzheimer’s and depression is murky, both diseases are major public health concerns. Among people 65 and older, one in eight has Alzheimer’s disease; an estimated one of 11 adults overall report depression. Current drugs can effectively combat depression in most cases, but nothing exists to prevent Alzheimer’s. right now, Alzheimer’s is the fifth leading cause of death in people 65 years and older. And unlike other major diseases such as heart disease and stroke, which caused fewer deaths in 2008 than in 2000, Alzheimer’s deaths rose by 66 percent in that time (see graph). With the oldest of the baby boomers turning 65 this year, that trend is expected to worsen.