Taking what could be an important step toward preventing Alzheimer's, scientists found that an experimental vaccine can largely ward off memory loss in mice stricken with a similar disease.
The vaccine is already being tested in people.
"This potentially could be a major breakthrough for us," said Zaven Khachaturian, senior science adviser to the Alzheimer's Association.
But he stressed that treatments that work in mice do not necessarily help people and that the mouse research did not deal with some key mental abilities lost in Alzheimer's, such as language and judgment.
The vaccine made headlines last year when scientists reported that it largely blocks the formation of protein deposits called amyloid plaques in the brains of mice. Such plaques are a hallmark of Alzheimer's.
But the next step was to find whether the vaccine makes any difference in the animals' mental functioning.
Two studies published in Thursday's issue of the journal Nature found that the vaccine does indeed make a difference.
The research was conducted by two independent research teams, centered at the University of South Florida in Tampa and the University of Toronto in Ontario, Canada.
The studies used strains of mice that develop lots of amyloid plaques in their brains, along with measurable memory deficits, because of the genes they carry.
The researchers used different versions of a procedure in which mice swam until they learned the location of an underwater platform. The animals were then tested to see how well they remembered where the platform was. Alzheimer's patients frequently have trouble remembering locations and how to get to destinations.
Both studies found that mice that had been repeatedly vaccinated performed markedly better than the untreated plaque-forming mice in the memory tests. On some occasions they did as well or nearly as well as ordinary mice.
University of South Florida researcher Dave Morgan said his vaccinated mice were slower to learn the platform location but eventually remembered it as well as ordinary mice did.
This past July, drug company scientists announced that preliminary results in human patients indicated the vaccine was safe. Those tests were not designed to assess any effect on symptoms.
Human tests are continuing under the sponsorship of Elan Corp. of Dublin, Ireland, and American Home Products Corp. of Madison, N.J. Neither company paid for the new mouse studies.
The researchers who carried out the mouse studies said it is not clear why the vaccine protects memory. For one thing, the research does not settle the question of whether the plaques actually cause the symptoms of Alzheimer's.
The vaccine was designed to make the mouse immune system attack amyloid-beta peptide, also called beta amyloid, a key component of the brain plaques in Alzheimer's. And both studies found that vaccinated mice had fewer and smaller amyloid plaques in their brains.
But Morgan noted that his treated mice still had a lot of plaques.
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