The secondary and cytotoxic BAs, lithocholic acid (LCA), and deoxycholic acid (DCA) increased non-significantly in MCI and AD compared with ND subjects (Figure ). Higher levels of LCA and DCA were previously noted in AD blood samples , suggesting LCA as putative biomarker for AD . Interestingly, 3-keto-LCA, the major metabolite of LCA, was found with statistically higher concentrations in AD compared to MCI and ND (bottom right of Figure ). This is a microbial metabolite, not previously reported in CSF, which could reflect the importance of the microbiota-gut-brain axis (MGBA) in neurodegeneration.