Poop transplant and Alzheimer's Disease

Wait a minute! What in the world is a poop transplant?

Believe it or not, there’s a thing called a fecal transplant: a doctor harvests the poop of a healthy person and infuses it into the colon of someone who is ill. It’s not really the feces that they’re after. Lots of bacteria are hiding inside the poop and they are the gold for which the doctors are mining. About 40 trillion bacteria are living inside your body right now. Most of them reside in your gut and don’t cause any health problems. Besides all those little bugs, you are composed of roughly 30 trillion human cells. Based on widely accepted democratic principles, if each cell in your body were given a vote, a bacteria would be elected president in a landslide.

 Why would anyone want any part of a fecal transplant? 

Well, there are good bacteria and bad bacteria. When your colon is dominated by agreeable bacteria, your body can be balanced in healthy harmony. 

When the evil bacteria rise to hegemony over your bowels, you are in trouble. There are several reasons why the balance between good and evil may get out of whack. As for many things in life, the problem may arise due to an unintended consequence of the putatively benign actions of someone in authority (in this case a doctor). If you are treated for an infection elsewhere in your body, the antibiotics that the doctor prescribes may decimate the healthful bacteria that are living peacefully in your bowels. Nature hates a vacuum, so the bad bacteria take over. 

One of the worst actors is called Clostridium difficile or C. diff. Most C. diff infections are treatable, but many are resistant to antibiotics (after all, that’s how they took over in the first place). C. diff produces toxins that can make you sick with diarrhea and colitis (colon inflammation). If a C. diff infection gets out of control, it may lead to toxic megacolon, which is as bad as it sounds. Toxic megacolon can be deadly because it puts you at risk for infection throughout the body, shock, and dehydration.

That’s where the fecal transplant comes in. In those cases, when C. diff is raging and cannot be stopped by the biggest antibiotic guns, the doctors become desperate to find a way to help. To win the fight, the doctors launch an indirect attack. The doctors find it impossible to decrease the numbers of bad bacteria, C. Diff, so they restore the balance by introducing good bacteria. Although it’s pretty gross, the doctors make a suspension of the poop of a healthy person (like a poop smoothie). They infuse the feces into the gastrointestinal tract of a patient who is ill, and the healthy person’s good bacteria are dragged along; passengers on the poop ride. The strong, healthful bacteria take up residence in the patient's colon and become the dominant force. They outcompete the C. Diff for resources and thereby beat back the illness. Those transplanted bacteria may flourish in their new home and help the patient’s body resist C. diff in the future. Hooray.

OK, but what does fecal transplant have to do with Alzheimer’s Disease?

I’m glad you asked. In 2023, Irish and Italian researchers investigated the relationship between gut microbes and Alzheimer’s Disease in a combined study between human beings and laboratory animals. The scientists recruited over a hundred volunteers (about half of whom had Alzheimer’s Disease and the rest were cognitively normal). The bugs in the gastrointestinal tracts of the Alzheimer’s cohort were out of whack: an imbalance between beneficial and harmful bacteria.  

The doctors then extracted poop from the humans and injected it into the colons of laboratory rats. Those rats who received fecal transplants from Alzheimer’s patients developed Alzheimer-like symptoms. What’s more, the unlucky poop recipients demonstrated brain abnormalities. The hippocampus (a part of the brain responsible for memory) of the affected rats produced fewer new neurons (brain cells), a process called neurogenesis. The researchers believe inflammation from bad bacteria in the bowels of affected animals harmed their cerebral function via the Gut-Brain Axis. 

If you’d like to learn how Gut Microbes may affect autism, please read https://brain2mind.substack.com/p/gut-microbes-and-autism