Two newly published studies led by Dr. Jennifer Rabin at Sunnybrook Research Institute (SRI) add to the accumulating evidence that vascular disease contributes to the development of Alzheimer’s disease dementia.
“The main theme of both studies is that people who have both Alzheimer’s disease and poor vascular health decline much more quickly than people who have only one of these conditions,” says Dr. Rabin, a scientist at SRI in the Hurvitz Brain Sciences Program.
There is growing evidence that vascular health and Alzheimer’s disease are closely intertwined, and that poor vascular health may promote the build-up of amyloid and tau in the brain, the two abnormal proteins associated with Alzheimer’s disease. “Preventing vascular disease may also help to prevent Alzheimer’s disease,” says Dr. Rabin.
The findings of the first study were published in Brain and the results of the second study were published in Neurology. Both are highly prestigious journals. Dr. Rabin, who was the only Canadian researcher involved in the studies, collaborated with U.S. colleagues to conduct the research.
Scientist Dr. Jennifer Rabin
What did you learn about the connection between CAA and Alzheimer’s disease?
The Brain study looked at a cerebrovascular condition known as cerebral amyloid angiopathy (CAA), which results from the build-up of amyloid in the blood vessel walls of the brain. When there is accumulating amyloid in the vessel walls it can cause vascular brain changes, such as small hemorrhages and blood flow problems. Although amyloid plays a central role in both CAA and Alzheimer’s disease, the two conditions are considered distinct.
The study is titled, “Cerebral amyloid angiopathy interacts with neuritic amyloid plaques to promote tau and cognitive decline.”
Dr. Rabin and colleagues from multiple U.S. centres asked the question: What influence does CAA have on the build-up of tau (the more detrimental hallmark pathology of Alzheimer’s disease) and cognitive decline, either alone or in combination with amyloid burden?
They analysed data from 1,722 autopsied subjects recruited from one of three long-running medical studies. Data included annual clinical and cognitive evaluations, along with neuropathology. The researchers tested associations between CAA, tau burden and cognitive decline, both independently and together with amyloid burden.
They found that the combination of CAA and higher amyloid levels were associated with the greatest tau burden and the fastest rates of cognitive decline.
“Not everyone with CAA has Alzheimer’s disease and not everyone with Alzheimer’s disease has CAA. But they do co-occur at a high rate,” says Dr. Rabin. “We found that if you have both of these conditions, you were much more likely to have tau burden and faster cognitive decline.”
How do classic vascular risk factors affect the brain?
The study in Neurology looked at whether classic vascular risk factors, such as obesity, high blood pressure, smoking and diabetes, leads to faster brain tissue loss and faster cognitive decline when they co-occur with amyloid.
The study is titled “Association of β-Amyloid and Vascular Risk on Longitudinal Patterns of Brain Atrophy.”
Dr. Rabin and colleagues from Massachusetts General Hospital analysed clinical and neuroimaging data from 196 subjects in the Harvard Aging Brain Study, a long-standing, community-based study.
They found that people who had multiple vascular risk factors and high levels of amyloid had greater rates of brain tissue loss and cognitive decline over time. “The take away,” says Dr. Rabin, “is that managing vascular risk factors may slow the progression of Alzheimer’s disease dementia.” This includes controlling blood pressure, lowering cholesterol, maintaining a healthy weight, and refraining from smoking. A good rule of thumb is that what’s good for the heart is good for the brain.
What do these results mean for patients and care providers?
These two studies provide greater support for the idea that vascular health and Alzheimer’s disease interact in ways that increase the likelihood of a dementia diagnosis. “These findings have implications for developing treatments for Alzheimer’s disease,” says Dr. Rabin, “because they suggest that vascular health should be taken into account. Treatments that target poor vascular health and Alzheimer’s pathology are likely to be the most effective.”
How you can get involved
If you are interested in getting involved in Dr. Rabin’s research studies, please send an email to cbhlab@sunnybrook.ca.
