The gut-brain axis is a bidirectional communication network that links the enteric and central nervous systems.

This network is not only anatomical, but it extends to include endocrine, humoral, metabolic, and immune routes of communication. Although bile acids may not be synthesized locally in the brain, the majority of brain bile acids are taken up from the systemic circulation. Since the composition of the brain bile acid pool may be regulated by the action of intestinal bacteria, it is possible that bile acids function as a communication bridge between the gut microbiome and the brain. This is an area where exciting new research may uncover the role of bile acids as neuroactive molecules.

There is growing evidence between the link in susceptibility of neurodegenerative conditions such as Alzheimer’s (AD) and Parkinson’s disease (PD) with Type 2 diabetes and obesity. BA regulation is disrupted in obese and Type 2 diabetic patients, altering bile acid NR and GCPR signalling pathways as well as causing changes to the gut microbiome that alter gut-liver-brain signalling. These disruptions may well be part of the complex pathways leading to neurodegenerative conditions and bile acids are now being considered as potential markers for prodromal diagnosis of both AD and PD.

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Bile acid receptors and signalling crosstalk in the liver, gut and brain

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Tauroursodeoxycholic acid in the treatment of patients with amyotrophic lateral sclerosis.

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Ursocholanic acid rescues mitochondrial function in common forms of familial Parkinson’s disease.

Heather Mortiboys, Jan Aasly and Oliver Bandmann. Brain 2013: 136; 3038–3050.

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Altered bile acid profile in mild cognitive impairment and Alzheimer’s disease: Relationship to neuroimaging and CSF biomarkers

Kwangsik Nho et al, Alzheimer’s & Dementia,https://doi.org/10.1016/j.jalz.2018.08.012.

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Gut Microbiota Dysbiosis Is Associated with Elevated Bile Acids in Parkinson’s Disease

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