Alzheimer’s disease (AD) is the most common form of dementia (disorder affecting the brain) in the western world. However, there is no cure available for this devastating neurodegenerative disorder. This disease is characterized by proteins called beta amyloid (Aβ) which build up in the brain to form structures called ‘plaques’ and ‘tangles’ (1). This leads to the loss of connections between nerve cells, and eventually to the death of nerve cells and loss of brain tissue. Since Alzheimer’s is a progressive disease, this means that gradually, over time, more parts of the brain will be damaged. As this happens, more symptoms develop and become more severe. Some of the symptoms of Alzheimer’s are memory loss, confusion, inability to learn new things, hallucinations and impulsive behavior (2).
But what does Alzheimer’s disease have to do with the gut microbiota?
Increasing evidence suggests that the gastro-intestinal tract is the bridge between microbiota and the central nervous system. As a matter of fact, a growing body of clinical and experimental evidence suggests that gut microbiota may contribute to aging and influence brain disorders (3). For instance, a new connection between gut microbiota and Parkinson’s disease has been reported in humans. In mouse models, studies report a role for the microbiota in the modulation of stress-related behaviors relevant to psychiatric disorders as mentioned in one of our previous blogs (You can read that blog here http://www.thegutguys.com/myhealth/the-worried-gut-can-gut-bacteria-influence-our-mood).
Similarly, recent studies have showed marked differences in the gut bacteria composition between mice suffering from Alzheimer's and healthy mice (4). Researchers also studied Alzheimer’s disease in mice that completely lacked bacteria to further test the relationship between intestinal bacteria and the disease. The results showed that mice without bacteria had a significantly smaller amount of beta amyloid plaques in the brain (recall: Beta-amyloid plaques are the lumps that form at the nerve fibres in cases of Alzheimer's disease).
Furthermore, in order to clarify the link between intestinal bacteria and the occurrence of the disease, the researchers transferred intestinal bacteria from diseased mice to germ-free mice (meaning mice free of bacteria), and discovered that the mice developed more beta-amyloid plaques in the brain compared to if they had received bacteria from healthy mice (4). Overall, that’s all a very scientific way to say that a healthier gut appears to lead to both a lower incidence of Alzheimer’s and a less severe form of the disease when it does occur.
These are very promising results and they have the potential for opening new area for the treatment and prevention of Alzheimer’s disease and ultimately other neurodegenerative disorders. In fact, researchers will continue to study the role of bacteria in the development of Alzheimer's disease, and test entirely new types of preventive and therapeutic strategies based on the modulation of the gut microbiota through diet and new types of probiotics.
1. Park, Laibaik, Ken Uekawa, Lidia Garcia-Bonilla, Kenzo Koizumi, Michelle Murphy, Rose Pitstick, Linda H. Younkin, Steven G. Younkin, Ping Zhou, Geroge A. Carlson, Josef Anrather, and Costantino Iadecola. "Brain Perivascular Macrophages Initiate the Neurovascular Dysfunction of Alzheimer AÎ² Peptides." Circulation Research (2017): n. pag.
2. Society, Alzheimer's. "Alzheimer's Disease." Alzheimer's Society. Alzheimer's Society, 11 Nov. 2016. Web.
3. O’Toole, P. W. & Jeffery, I. B. Gut microbiota and aging. Science 350, 1214–1215, (2015).
4. Harach, T., N. Marungruang, N. Duthilleul, V. Cheatham, K. D. Mc Coy, G. Frisoni, J. J. Neher, F. FÃ¥k, M. Jucker, T. Lasser, and T. Bolmont. "Reduction of Abeta Amyloid Pathology in APPPS1 Transgenic Mice in the Absence of Gut Microbiota." Scientific Reports 7 (2017): 41802.