As observed with the primary conjugated BAs, the secondary conjugated BAs showed lower trends in the AD compared to the MCI group (Figure ). Significantly lower concentrations of GUDCA were found in AD compared to the MCI group, in line with a previous study identifying GUDCA as a potential blood marker for early diagnosis that could predict the onset of AD or MCI with 2-3 years and 90% of accuracy . This highlights the importance of the MCI group to study early disease biomarkers. While the average GCDCA concentration across the 30 samples was 1.92 nM, the average of GCDCA-S was 871.56 nM. This trend was also observed for GDCA (0.60) and GDCA-S (866.73), see Figure . Sulfation, catalyzed by SULT2A1 in humans, is an important detoxification pathway of BAs. The resulting sulfated BAs are less toxic and more soluble, leading to reduced intestinal absorption and enhanced fecal and urinary excretion . This suggests that the brain may utilize sulfation to mitigate the BAs toxicity, as SULT2A1 is expressed not only in the liver but also in the brain .