Alzheimer’s Link with Gut Health Revealed by New Study

Scientists at Florida State University (FSU) have discovered a potential link between gut bacteria and the likelihood of developing Alzheimer’s disease.

An estimated 6.7 million older adults have Alzheimer’s disease in the U.S., according to the Centers for Disease Control and Prevention—a figure that is expected to double by 2060.

The most common type of dementia, the disease involves memory loss and cognition issues that gradually get worse over time as the brain deteriorates.

But FSU scientists have discovered a potential reason why some people might be more likely to develop Alzheimer’s, paving the way for potential preventative treatments—and it’s all to do with the gut.

The gut is full of microorganisms, including many different strains of bacteria and yeasts. A healthier gut has a lot of these microorganisms, a wide variety of them, and a good balance between beneficial and less beneficial types.

But sometimes, guts can become out of balance. This might be because of the diet, stress, or a course of antibiotics, which can kill off gut bacteria, the good and the bad.

After a course of antibiotics, with lower all-round levels of bacteria in the gut, some strains can proliferate more than others and create imbalance—dysbiosis—in the gut.

FSU scientists found a link between Klebsiella pneumoniae, common bacteria that has developed significant resistance to antibiotics, and the development of Alzheimer’s disease.

K. pneumoniae is notorious for causing infections in hospitalized patients, often after courses of antibiotics.

The scientists found that, after antibiotics, K. pneumoniae may overgrow in the gut, pass through the gut wall into the bloodstream, and then travel to other organs, including the brain, where it can create inflammation.

Neuroinflammation is recognized as a prominent factor that can lead to Alzheimer’s disease.

“Hospital-acquired and septic infections are one of the risk factors that may increase the predispositions to future neuroinflammatory and neurocognitive impairments, especially in older adults,” said last author Ravinder Nagpal, assistant professor at FSU and director of FSU’s Gut Biome Lab, in a statement.

“Hospitalizations and ICU [intensive care unit] stays, combined with antibiotic exposure, may lead to a further decline in microbiome diversity that leaves older adults at high risk not only for digestive issues but also for extra-intestinal pathologies such as neurodegenerative disorders through a dysregulation of the gut-brain axis.”

The Florida scientists discovered this by experimenting on mice, testing the microbes in their gut, blood and brain, and then testing their brain and memory function.

Mice who were given antibiotics were likely to develop gut dysbiosis, they found, and then fed the mice K. pneumoniae broth and found it took hold more easily in the imbalanced guts.

Those mice who developed infections were then found to have severe abscesses on and around the brain, brain inflammation, and worse cognitive and memory function.

The scientists concluded that disruptions to the gut could lead to problems with the brain, including the development of neurodegenerative diseases such as Alzheimer’s.

This study was published in scientific journal The Journal of Infectious Diseases in September.

It was funded by the Infectious Disease Society of America and the Florida Department of Health.

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Reference

Park, G., Kadyan, S., Hochuli, N., Salazar, G., Laitano, O., Chakrabarty, P., Efron, P. A., Zafar, M. A., Wilber, A., Nagpal, R. (2024). An Enteric Bacterial Infection Triggers Neuroinflammation and Neurobehavioral Impairment in 3xTg-AD Transgenic Mice, The Journal of Infectious Diseases 230(2). http://dx.doi.org/10.1093/infdis/jiae165