A small, early-stage clinical trial has identified a drug that destroys plaque buildups in the brain associated with Alzheimer’s disease. Because scientists believe these plaques may be responsible for memory loss and cognitive decline, the findings have been heralded as a potential game changer for Alzheimer’s research—although practical applications are likely still several years away, at least.

The exact cause of Alzheimer’s disease is unknown, but studies have shown that sticky clumps of protein, called amyloid-beta plaques, tend to form in the brains of patients up to 15 years before they start to exhibit cognitive symptoms. The problem? Some people with no memory problems have been shown to have brain plaques, so it's not as clear cut as, say, smoking causes cancer. However, much of the pharmaceutical research into potential treatments has focused on ways to prevent or eliminate these plaques.

The Massachusetts-based company Biogen may have found a way to do so. In a clinical trial, they tested various doses of the drug aducanumab on 125 patients with early-stage Alzheimer’s disease, giving them monthly IV infusions over 54 weeks. (Aducanumab is a monoclonal antibody, a molecule produced in a lab to mimic human immune system proteins.) Another 40 patients got placebo infusions.

At the end of the study, brain scans revealed that the patients who were given the drug had less plaque than when they’d started, and those who were given the highest doses were nearly plaque-free. Patients who got the placebo, on the other hand, experienced almost no brain changes.  

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What’s more, these plaque reductions may have kept Alzheimer’s symptoms from getting worse. "While patients in the placebo group exhibited significant cognitive decline, cognitive ability remained distinctly more stable in patients receiving the antibody," said co-author Roger M. Nitsch, MD, director of the Institute for Regenerative Medicine at the University of Zurich, in a press release. (Although these types of studies aren't designed to determine if treatments work—just that they are safe for people—the researchers did give participants questionnaires to test their cognitive abilities.) 

This finding is a big deal, says Eric M. Reiman, MD, executive director of the Banner Alzheimer's Institute in Phoenix. In a commentary published along with the research in the journal Nature, Dr. Reiman—who was not involved in the study—writes that the results were “unusually striking,” and that they support the hypothesis that plaque really does contribute to the development of Alzheimer’s symptoms.

“If these preliminary cognitive findings are confirmed in larger and more definitive clinical trials, which are now underway, it would provide a shot in the arm in the fight against Alzheimer’s disease,” he writes.

However, he cautions, “although the authors’ additional cognitive findings are encouraging, they are not definitive.” If further research shows that reducing plaque does not affect the progression of Alzheimer’s disease, he explains, this drug—and others like it—would likely prove ineffective at stopping symptoms like memory loss. “It would be prudent to withhold judgment about aducanumab’s cognitive benefit until results from the larger trial are in,” he writes.

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Biogen’s findings are the result of a phase 1b clinical trial. On the path to new drug development, these are typically some of the first studies conducted with human volunteers, and involve only a small number of people.

Even when phase I results are promising, larger phase II and III trials are still required before a drug can be considered safe and effective, and ultimately approved for consumer use. The study authors also note that side effects from the drug must be taken into account: In their study, 20 patients dropped out because of headaches and fluid buildup in the brain, which can be dangerous. What's more, many drugs for Alzheimer's disease that have looked promising in the early stages of research have turned out to be disappointing after further study.

Aducanumab is now being studied in two ongoing trials with about 2,700 participants total. So while these preliminary results were just a first step in a much longer process, Dr. Nitsch says he is optimistic that it will lead to even bigger steps in the right direction.

Dr. Reisman agrees. In his commentary, he advocates for more research to confirm that a plaque-busting drug can indeed slow cognitive decline. That, he writes, “would be a game-changer for how we understand, treat, and prevent Alzheimer’s disease.”