Comprehensive metabolomics profiling reveals novel biomarkers and pathways for early detection of Alzheimer's disease.

Alzheimer's disease is a multifactorial neurodegenerative disorder marked by cognitive decline, synaptic dysfunction, and metabolic alterations. This study investigated disease-associated profiles in the Indian population using integrated clinical, metabolomic, and plasma biomarker analyses. We enrolled 25 clinically diagnosed patients (mean age: 61.20 ± 7.76 years) and 25 cognitively healthy controls (mean age: 60.56 ± 7.48 years). Cognitive and neuropsychiatric assessments included Addenbrooke's Cognitive Examination-III, Clinical Dementia Rating-Global, and Patient Health Questionnaire-9 for patients, and Montreal Cognitive Assessment, Clinical Dementia Rating-Global, and Patient Health Questionnaire-9 for controls. Plasma metabolomics was performed using liquid chromatography-mass spectrometry, and targeted ELISA quantified amyloid beta 40, amyloid beta 42, phosphorylated tau181, phosphorylated tau217, neurofilament light chain, apolipoprotein E, APOE4, 8-hydroxy-2'-deoxyguanosine, C-reactive protein, brain-derived neurotrophic factor, and glutamate. Statistical analyses included principal component analysis, volcano plots, receiver operating characteristic curves, pathway enrichment, and correlation analyses. Patients showed reduced cognition (median Addenbrooke's Cognitive Examination-III: 26). Clinical Dementia Rating-Global scores (1.44 ± 0.65 versus 0.24 ± 0.25; P < 0.0001) and Patient Health Questionnaire-9 scores (4.88 ± 4.21 versus 0.20 ± 0.50; P < 0.0001) were higher than controls. Principal component analysis revealed distinct metabolic clustering with 75 altered metabolites. Volcano analysis identified six upregulated (leucine, ascorbic acid, guanine) and 14 downregulated metabolites (valine, nicotinamide, octadecanedicarboxylic acid). Receiver operating characteristic curves highlighted octadecanedicarboxylic acid (AUC = 0.917), prolinamide (AUC = 0.908), 2-phosphoglycerate (AUC = 0.858), nicotinamide (AUC = 0.848), leucine (AUC = 0.768), and ascorbic acid (AUC = 0.748). Pathway enrichment indicated disruptions in branched-chain amino acid metabolism, nicotinamide metabolism, the tricarboxylic acid cycle, and neurotransmitter pathways. Biomarker analysis revealed elevated amyloid beta 40, amyloid beta 42/40 ratio, phosphorylated tau181, phosphorylated tau217, phosphorylated tau217/amyloid beta 42 ratio, neurofilament light chain, APOE4, C-reactive protein, and 8-hydroxy-2'-deoxyguanosine, with reduced brain-derived neurotrophic factor (all P < 0.05). Significant correlations included eupatilin with phosphorylated tau217 and 8-hydroxy-2'-deoxyguanosine, glyceraldehyde with brain-derived neurotrophic factor, guanine with APOE4, and valine inversely with phosphorylated tau181. This study identifies distinct metabolic (octadecanedicarboxylic acid, prolinamide, leucine, ascorbic acid) and biomarker profiles (phosphorylated tau217, 8-hydroxy-2'-deoxyguanosine, brain-derived neurotrophic factor) in Alzheimer's disease. Disrupted pathways linked to neuroinflammation and oxidative stress support the potential for integrated early detection strategies. Despite the small cross-sectional cohort, findings highlight the need for longitudinal, multi-centric validation.