The gut microbiota-derived metabolite trimethylamine N-oxide is elevated in Alzheimer's disease

BackgroundTrimethylamine N-oxide (TMAO), a small molecule produced by the metaorganismal metabolism of dietary choline, has been implicated in human disease pathogenesis, including known risk factors for Alzheimer's disease (AD), such as metabolic, cardiovascular, and cerebrovascular disease.MethodsIn this study, we tested whether TMAO is linked to AD by examining TMAO levels in cerebrospinal fluid (CSF) collected from a large sample (n=410) of individuals with Alzheimer's clinical syndrome (n=40), individuals with mild cognitive impairment (MCI) (n=35), and cognitively-unimpaired individuals (n=335). Linear regression analyses were used to determine differences in CSF TMAO between groups (controlling for age, sex, and APOE epsilon 4 genotype), as well as to determine relationships between CSF TMAO and CSF biomarkers of AD (phosphorylated tau and beta-amyloid) and neuronal degeneration (total tau, neurogranin, and neurofilament light chain protein).ResultsCSF TMAO is higher in individuals with MCI and AD dementia compared to cognitively-unimpaired individuals, and elevated CSF TMAO is associated with biomarkers of AD pathology (phosphorylated tau and phosphorylated tau/A(42)) and neuronal degeneration (total tau and neurofilament light chain protein).ConclusionsThese findings provide additional insight into gut microbial involvement in AD and add to the growing understanding of the gut-brain axis.