WASHINGTON (AP) - In what may be a new warning sign about a once-promising therapy for Alzheimer's disease, researchers report that in animal studies a vaccine that clears the brain of toxic deposits also tends to double the risk of stroke.
Researchers have been intensively studying the idea that the brain-destroying disease could be controlled by removing deposits of a toxic substance called amyloid beta that accumulates in the brains of Alzheimer's disease patients, filling the spaces between cells.
While researchers are uncertain if amyloid beta is the cause of Alzheimer's or the result of another mind-destroying process, some earlier animal studies found that a vaccine that prompts the body to remove amyloid beta was able to stop progression of the disease and even restore some brain function.
The promising results led an Irish pharmaceutical firm, Elan Corp., to test an amyloid beta vaccine on 360 human patients, but the clinical trial was suspended early this year after 15 patients developed inflammation of tissues in the brain. Elan has since said it would no longer test the original vaccine, but will continue to monitor patients who received it.
Now a new study, appearing Friday in the journal Science, suggests that a vaccine against amyloid beta may have other problems - a significant increase in bleeding in the brain.
Swiss, German and American researchers used a lab mouse strain that had been genetically manipulated to develop the major symptoms of Alzheimer's disease, including the formation of amyloid beta.
The mice were injected with a vaccine that caused their bodies to make antibodies against amyloid beta. After five months, the researchers said there was a 23 percent reduction of the amyloid beta in the test mice compared with animals that did not receive the vaccine.
However, the test mice also had twice the number of cerebral hemorrhages, or bleeding in the brain, compared with mice that did not get the vaccine. Additionally, the researchers found six major blood clots among the immunized mice, versus only one among the control mice.
The findings, said co-author Dr. Paul M. Mathews of New York University School of Medicine, suggest that scientists still lack a clear appreciation of the possible side effects of Alzheimer's vaccine therapy.
"Up to this point, all of the animal studies have been very promising," said Mathews. "This is the first study to show any serious side effects in mice."
Mathews said the mouse strain used in his study is a closer mimic to the way Alzheimer's appears in the human brain than animals used in earlier studies. He said the mice had deposits of amyloid beta on blood vessels, a very common characteristic of human patients.
Finding this new side effect, he said, suggests that the human trials of Alzheimer's vaccine "were premature."
"We need to move back into animals and sort this out," said Mathews. "We need to develop antibodies (vaccines) that don't cause this problem. Otherwise, I don't think this (type of therapy) will work in humans."
Bill Thies, vice president for medical and scientific affairs of the Alzheimer's Association, said the new study "is an interesting paper and something that we should look at carefully."
But he said Alzheimer's vaccine therapy remains promising and research should be pursued vigorously.
"We are continuing to unravel some of the nuances of it," said Thies. "Whether it ends up being a useful therapy or not is still an open question, but it has enough promise that a lot of people are still working on it."
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