The Microbiota–Gut–Brain Axis and Alzheimer’s Disease: Neuroinflammation Is to Blame?

Abstract

For years, it has been reported that Alzheimer’s disease (AD) is the most common cause of dementia. Various external and internal factors may contribute to the early onset of AD. This review highlights a contribution of the disturbances in the microbiota–gut–brain (MGB) axis to the development of AD. Alteration in the gut microbiota composition is determined by increase in the permeability of the gut barrier and immune cell activation, leading to impairment in the blood–brain barrier function that promotes neuroinflammation, neuronal loss, neural injury, and ultimately AD. Numerous studies have shown that the gut microbiota plays a crucial role in brain function and changes in the behavior of individuals and the formation of bacterial amyloids. Lipopolysaccharides and bacterial amyloids synthesized by the gut microbiota can trigger the immune cells residing in the brain and can activate the immune response leading to neuroinflammation. Growing experimental and clinical data indicate the prominent role of gut dysbiosis and microbiota–host interactions in AD. Modulation of the gut microbiota with antibiotics or probiotic supplementation may create new preventive and therapeutic options in AD. Accumulating evidences affirm that research on MGB involvement in AD is necessary for new treatment targets and therapies for AD.

The Role of Gut Microbiota and Gut–Brain Interplay in Selected Diseases of the Central Nervous System

“…It has been demonstrated that the production of α-synuclein within the intestines and its accumulation in the brain of examined rodents is intensified, which further prompts microgliosis and astrogliosis. Moreover, the rat brains showed an increased expression of TLR-2, TNF-α, and IL-6, which may indicate that amyloids produced by bacteria provoke α-synuclein aggregation and, as a result, an innate immune system response [ 109 , 110 ]. Another microbial metabolite, LPS, might be a crucial factor in the pathophysiology of PD, similarly to AD.…”

Novel Therapeutic Approaches for Alzheimer’s Disease: An Updated Review

“…The composition of the gut microbiota affects the gut–brain communication and brain function by synthesizing various neurotransmitters and neuromodulators [ 230 ]. Dysbiosis of the gut microbiota leads to an overproduction of LPS in the gut, which increases permeability to the BBB [ 231 ].…”

Regulation of Intestinal Microbiota as a Therapeutic Target for Neuroinflammatory Diseases in Persistent COVID

“…The emission of the intestinal microbiota modulates the immune system. In return, microbial symbionts control the maturation and function of the immune system (19)(20)(21). By way of conclusions, we can say that it is essential to modulate the composition and function of the intestinal microbiota in subjects with persistent COVID through natural products, such as probiotics, as a strategy to promote immune function and thus modulate inflammatory responses.…”