Gut-Microbiota-Brain-Axis, Leaky Gut, Leaky Brain: Pathophysiology of Second Brain Aging and Alzheimer’s disease- A Neuroscientific Riddle

Alzheimer’s disease (AD) is one of the most common neurodegenerative illnesses. However, how Gut-Microbiota plays a role in the pathogenesis of AD is not well elucidated. The purpose of this literature review is to summarize and understand the current findings that may elucidate the gut microbiota role in the pathogenesis of AD. A literature review of all the relevant papers knows to the author was conducted. Relevant articles, abstracts and research papers were collected from well-accepted web sources like PubMed, PMC, and Google Scholar. Recent studies have shown that Gut-microbiota has an important role in the progression of AD, via Gut-Microbiota-Brain Axis. The onset of AD supports ‘Hygiene Hypothesis’ which showed that AD may begin in the Gut causing dysbiosis which interferes with intestinal barrier by releasing pro-inflammatory cytokines and makes it way up to the brain via Blood-Brain-Barrier (BBB). Molecular mechanisms lipopolysaccharides and serotonin kynurenine (tryptophan) pathways have a direct association with inflammation, immune system, neurodegeneration, and AD. The studies focusing on the second brain aging of the intestine, dysbiosis, and the ultimate complications of dysbiosis link to the brain via Gut-brain axis. This review will summarize the current findings on gut-microbiota and second brain aging which have crucial role in neurodegeneration and Alzheimers disease. Which further studies to explore the therapeutic effects of probiotics in AD and cognitive enhancement should be warranted to provide significant clinical and practical value.