For decades, the process that leads a brain down the path of Alzheimer’s disease has remained a mystery. While researchers found some clues, their efforts were hampered by the challenge of growing brain cells called neurons effectively in the lab and by their ability to image the brain in enough detail. As a result, many researchers were stuck using dead brains to study Alzheimer’s rather than examining the living tissue. Recent research fixed the problem of growing neurons in the lab for testing and now new research has improved the way we image the brain.
What do we know about Alzheimer’s?
Alzheimer’s is a disease that affects the brain and leads to death of neurons and a slow loss of mental function. Symptoms start most obviously with memory difficulties, but other more subtle problems associated with how the brain processes information are present as well. In the very early stages, these changes in mental function are called “mild cognitive impairment” or MCI because a person is still mostly functional but has some minor problems. Those with MCI often progress to Alzheimer’s years later as their brain declines.
Past research had shown that two proteins called tau and β-amyloid (Aβ) were involved in the death of neurons in a brain with Alzheimer’s. While the details are still being worked out, it seems like Aβ starts to show up in the brain first and helps tau build up as well. This buildup chokes the normal functioning of neurons and they eventually die. As neurons die, brain function is lost.
How is imaging involved?
MRI machines provide the best images of a living brain. Using special chemicals called contrast, doctors can see both the structure of the brain and the blood vessels running through it. One reason this is possible is because the brain has a protective barrier on its blood vessels not present elsewhere in the body. The brain has sealed these pipes so that only very specific things can get across while toxins and other harmful chemicals are kept out. Some contrast can pass through this barrier and others can’t. Past research had noticed that contrast that shouldn’t be able to cross this barrier was crossing into the brain of those with Alzheimer’s. Unfortunately, the images were never of high enough quality to see how and where this was happening.
What did the research show?
The authors of the current study were able to improve the quality of their MRI images so that they could zone in on which areas of the brain were experiencing these leaks. They looked at the brains of healthy people aged 23 to 91 and compared them to a group of older adults with MCI. They found that blood vessels got leakier as people aged with more contrast ending up in the brain. But the effect was dramatic in people with MCI. These individuals had 60% more leakage in their brain than people with normal brain function of the same age, especially in the hippocampus where memories are made and stored, which often suffers damage first in Alzheimer’s.
On further investigation, the researchers found that tau and Aβ damage cells that normally help to prevent leaking in the brain and keep vessels sealed. They think that small amounts of leakage can be tolerated as a person gets older, but too much leads to dysfunction, damage and potentially death of neurons in key areas.
What does this research mean for you?
This research represents another step toward understanding Alzheimer’s. As the picture fills out, researchers will better understand what kinds of treatments might be helpful and will target drugs to block the progression and perhaps even the beginning of Alzheimer’s disease, an illness that currently has no effective treatment and no cure.