Time-dependent circulating metabolic changes and key regulatory pathways in Alzheimer's disease: A combined animal model and public database study.

Early diagnosis remains a major challenge in Alzheimer's disease (AD), as clinical symptoms often appear after irreversible pathological progression. This study aimed to identify early diagnostic biomarkers and clarify metabolic regulatory mechanisms in AD by integrating metabolomic profiling from a mouse model with validation using public human datasets. AD models were established in 42 C57BL/6J mice by intraperitoneal injection of D-galactose (120 mg/kg) combined with intragastric administration of aluminum chloride (20 mg/kg) for 8 weeks. Plasma samples were collected at weeks 0, 3, 6, and 8 for untargeted metabolomic profiling. Public plasma/cerebrospinal fluid metabolomic datasets and brain transcriptomic datasets from AD patients were further analyzed for validation. Time-dependent metabolic alterations were observed in AD mice, characterized by predominant metabolite depletion at weeks 3-6 and compensatory accumulation at week 8. The metabolic profile of AD mice was clearly separated from that of controls at week 8. Nicotinamide metabolism and sphingosine-related pathways showed dynamic dysregulation during AD progression. Notably, nicotinamide and sphingosine were persistently increased in AD mice and were also elevated in plasma samples from AD patients, whereas metabolites such as N,N-diethyl-m-toluamide were decreased. Transcriptomic analysis revealed abnormal expression of key genes involved in nicotinamide metabolism (NMNAT1 and SIRT1) and sphingosine metabolism (SPTSSA and SPHK1) in brain tissues from AD patients. In conclusion, AD is characterized by stage-dependent metabolic dysregulation, featuring early depletion followed by late compensation. Dysregulated nicotinamide and sphingosine metabolism may contribute to AD pathogenesis, and related metabolites and regulatory genes may serve as potential diagnostic biomarkers and therapeutic targets.