Abstract
Alzheimer's disease (AD) is a neurodegenerative condition characterized by cognitive decline and associated metabolic disturbances, including altered amino acid profiles. This study investigated the effects of probiotic supplementation with Lactobacillus rhamnosus HA-114 and Bifidobacterium longum R0175 on serum amino acid levels in adults with mild to moderate AD. In a 12-week, randomized, double-blind, placebo-controlled trial, 60 participants (aged 50-90 years) were assigned to three groups: L. rhamnosus (n = 20), B. longum (n = 20), or placebo (n = 20). Serum amino acids were analyzed using High-Performance Liquid Chromatography (LC). Changes in total amino acids, Branched Chain Amino Acids (BCAAs), and aromatic amino acids (AAAs) were assessed as the primary outcomes. A significant interaction effect was found between time and group for serum amino acids. Compared to placebo, the B. longum group showed a significant increase in total amino acids (difference: 2132.67 µmol/L, 95% CI: 464.06-3801.28; p = 0.01), BCAAs (difference: 255.15 µmol/L, 95% CI: 53.01-457.30; p = 0.01), and AAAs (difference: 374.34 ng/ml, 95% CI: 57.45-691.23; p = 0.02). The L. rhamnosus group also showed a significant increase in BCAAs compared to placebo (difference: 206.08 µmol/L, 95% CI: 3.94-408.23; p = 0.04). The greatest improvements were consistently observed in the B. longum group across all primary outcome measures. Probiotic supplementation, particularly with B. longum, significantly improved serum amino acid profiles in patients with mild to moderate Alzheimer's disease. These findings support the potential of specific probiotic strains to address metabolic imbalances in AD through gut-brain axis modulation. Trial Registration: IRCT number: 20210513051277N1 (2021-05-27).