Microbes may trigger Alzheimer’s Disease.
A fascinating update on Alzheimer’s Dementia has just been published by James Hill and colleagues in Frontiers in Aging.
AD is a lethal form of brain degeneration. It is currently incurable, and is now one of the major causes of death in old age.
Advanced AD shows many kinds of pathology in the brain, including cell death, immune dysfunction, protein tangles (plaques), inflammation, changes in gene expression and molecular waste products. In other words, the advanced AD brain is a biological mess. Behaviorally, AD patients have trouble recognizing family members and doing other everyday tasks.
The fundamental question is what causes AD to take over a perfectly healthy brain — because many people grow older with no sign of AD. The traditional answers come from examining AD victims using brain imaging, and from brain samples after death. AD brains show a great many protein tangles (called “tau plaques,” after the Greek letter “t”). Tau plaques do interfere with normal neural signaling in the brain. But are they causal? Or are tau plaques just a byproduct of other disease processes in the brain?
Like our bodies, our brains are constantly assaulted by toxins, bacteria, viruses, molecular waste products, emotional stress, overwork, injuries, oxygen lack, glucose overload, and nutrient deficiencies.
Like our bodies, our brains maintain a delicate balance with trillions of micro-organisms. Our stomachs and intestines contain whole ecosystems of microbiota, tiny organisms that may benefit us (like yogurt) or that may do harm (like tapeworms). The brain has an extra protective barrier of densely packed cells, called the blood-brain barrier (BBB). But the BBB can develop leaks.
For many years stomach ulcers were thought to be due to stress, because experiments showed that stressed monkeys developed more stomach ulcers than stress-free monkeys. Then it turned out that stressed monkeys provided a better growth medium for the bacterium H. pylori. Stomach ulcers have multiple factors, but H. pylori is often the critical one, the one that sets off the disease more than any other. Ulcers are a multi-factorial disease; and now it looks like AD may be similar. Today, antibiotics are an effective first-line treatment for ulcers. Ulcers are therefore an excellent example of how biomedicine works, because many disorders are multifactorial, showing that even if there are a dozen big factors, some single factor can still be the most decisive one.
Your old car may have rusty wheels and worn tires, the battery may be low and the oil full of gummy gook; but the critical problem may be the worn transmission that finally stops the car in its tracks.
Hill and colleagues now propose that microbes may be the key to AD. This has been shown in some patient groups, although the causal role of microbes is not clear. Microbes multiply fast wherever brain tissue is damaged, even by a physical injury.
1. AD is associated with fungal infections.
2. .. and with herpes simplex.
3. … and with prion diseases like the “Mad Cow” particle.
4. … and with C. pneumoniae, the pneumonia bug.
5. … and even with the HIV virus.
6. … plus protozoan parasites like t. gondii.
7. … Also tiny plant viruses called viroids, and RNA fragments called micro RNA’s.
9. … plus the hepatitis virus.
Is that enough for you?
Now this may seem ridiculously complicated.
But remember stomach ulcers. In the beginning it looked like dozens of factors played a role, but in the end, the biggest clout was carried by H. pylori. Knock out H. pylori with an antibiotic, and most of the other problems go away.
Again, it’s like your old car. Keep up regular lube and oil jobs, rotate the tires, and it might last twice as long.
Many researchers are therefore looking at the “microbiota” (tiny living things) that could impact the brain.
Hill et al write that “Virtually every type of microbe known has been implicated in contributing to the … AD process.”
Still, there are a lot of microbiota in your body, estimated at 10 with 14 zeros. Some may be penetrating the brain under some conditions. The brain is surrounded by a dense tissue filter called the Blood Brain Barrier. But in AD the BBB often gets leaky.
So – it’s not that we don’t know what aggravates AD —rather, far too many things play a role.
The big question is: Could AD have some single “magic bullet,” like H. pylori in the case of stomach ulcers?
The answer might lie in some of those 10/14 microbiota making a riotous living in your gut.
With a little luck and a lot of hard work, we might find the answer.
It could even happen soon.