The Relationship Between Microbiota and Alzheimer’s Disease

Abstract

The term microbiota refers to the micro-organisms that interact with the host from birth to death. These interactions can reach the brain via the bloodstream or the gut-brain nervous system. The microbiota performs important beneficial functions, such as contributing to digestive processes, breaking down toxins and creating defense mechanisms against pathogenic bacteria. However, this positive situation only takes place when the microbiota is also positive, i.e. when the probiotics, known as eubiosis, are dominant. Factors such as nutritional habits, age and the use of antibiotics can impair the balance of the microbiota and lead to a situation where harmful microorganisms, known as dysbiosis, are dominant in the gut. In this case, the production of many microbial products that are normally beneficial to the body, such as neurotransmitters and some short-chain fatty acids, reduces and pathogenic metabolites are produced. In the case of dysbiosis, intestinal permeability increases, allowing harmful pathogenic metabolites to enter the bloodstream and even reach the brain via the bloodstream. For these reasons, prolonged dysbiosis is known to pave the way for many diseases such as depression, anxiety, schizophrenia, autism, diabetes, and Alzheimer’s disease. Alzheimer’s disease is characterized by the death of nerve cells in the brain and loss of cognitive abilities. The disease is associated with amyloid plaques and tau protein. It has been argued that disruption of the intestinal microbiota may contribute to the pathology of Alzheimer’s disease and may also have therapeutic potential. Amyloid production may be triggered by the intestinal microbiome, causing a way for the studies on Alzheimer’s disease. This review examines the relationship between the intestinal microbiota and Alzheimer’s disease.