Immune–proteo–metabolomic changes link to Aβ and tau pathology in Alzheimer disease

INTRODUCTION: Tryptophan metabolism is increasingly implicated in Alzheimer's disease (AD), particularly through aryl hydrocarbon receptor (AhR) ligands that influence neuroinflammation. However, their relationships with core AD pathology—amyloid-β (A) and tau (T) deposition—and associated immune–proteomic alterations remain unclear. METHODS: We performed integrative multi-omics/high-dimensional profiling of cerebrospinal fluid (CSF) and peripheral blood from A-T- (n = 19) and A+T+ (n = 35) individuals, classified based on CSF Aβ and pTau181 levels. Analyses included targeted metabolomics, mass cytometry, and NULISA-based proteomics, and inter-compartmental correlation analysis. Brain-derived tryptophan catabolism was investigated using single-nucleus RNA sequencing (snRNA-seq). RESULTS: Thirteen differentially expressed CSF proteins in A+T+ individuals correlated positively with tryptophan metabolites and pyroglutamate, and negatively with regulatory T cells, isobutyrate, and dendritic cells. Similar patterns were observed in blood. snRNA-seq suggested partial brain origin of metabolites. DISCUSSION: Our findings highlight conserved immune–metabolic–proteomic signatures in AD and implicate tryptophan metabolism as a cross-compartmental factor relevant for biomarker and therapeutic development.