Clearing amyloid beta shows no significant impact on dementia severity

Drugs that target amyloid beta proteins in the brain likely have no clinically meaningful positive effects, while increasing the risk of bleeding and swelling in the brain, a new Cochrane review has found.

People with Alzheimer's disease have high levels of a protein known as amyloid beta in their brains, detectable before symptoms begin, but its role in disease progression is uncertain. Drugs have been developed to remove these proteins from the brain, under the theory that this would prevent or slow disease progression.

The new review examined data from 17 clinical trials with a total of 20,342 participants, all looking at the impact of anti-amyloid drugs on people with mild cognitive impairment or mild dementia due to Alzheimer's disease. Proponents of these drugs have theorised that they would be more effective at these earlier stages before the disease has progressed.

Absolute effects "well below clinical threshold"

The research found that the absolute effects of anti-amyloid drugs on cognitive decline and dementia severity were absent or trivial, falling well below established thresholds for the minimum clinically important difference.

"Unfortunately, the evidence suggests that these drugs make no meaningful difference to patients," says lead author Francesco Nonino, neurologist and epidemiologist at the IRCCS Institute of Neurological Sciences of Bologna, Italy.

There is now a convincing body of evidence converging on the conclusion that there is no clinically meaningful effect. While early trials showed results that were statistically significant, it is important to distinguish between this and clinical relevance. It is common for trials to find statistically significant results that do not translate into a meaningful clinical difference for patients."

Francesco Nonino, IRCCS Institute of Neurological Sciences

In addition to the absence of clinically meaningful effects, the review found that anti-amyloid drugs likely increase the risk of swelling and bleeding in the brain. This was observed in brain scans without any apparent symptoms for most patients, although any long-term effects remain unclear since reporting of symptoms was inconsistent across trials.

Future research should focus on other pathways

On the basis of the evidence, the authors conclude that future trials targeting amyloid beta removal are unlikely to provide clear benefit to patients. They found that these drugs do successfully remove amyloid proteins from the brain, but this does not translate into meaningful clinical benefit. They recommend that future research on Alzheimer's treatment should focus on other mechanisms, with numerous studies ongoing in other directions.

"I see Alzheimer's patients in my clinic every week and I wish I had an effective treatment to offer them," says senior author Edo Richard, Professor of Neurology at Radboud University Medical Centre. "Existing approved drugs offer some benefit for some patients, but there remains a high unmet need for more effective treatments. Sadly, anti-amyloid drugs do not offer this and bring additional risks. Given the absence of correlation between amyloid removal and clinical benefit, we need to explore other pathways to help address this devastating disease."