Raman Spectroscopic Identification of Biochemical Alterations in Alzheimer’s Disease Brain Tissue

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder marked by chronic inflammation, neuronal loss, and continuous decline in memory and cognitive function. Raman Spectroscopy (RS) offers a powerful, label‑free approach for detecting early biochemical alterations in AD by generating highly sensitive molecular fingerprints. This capability is particularly valuable for identifying subtle changes associated with protein misfolding, lipid dysregulation, and oxidative stress, key processes underlying AD onset and progression. In our study, full‑spectrum RS revealed clear biochemical distinctions between control and AD brain tissues, as well as between Braak IV and Braak VI AD stages. Multivariate analytical methods, including Singular Value Decomposition (SVD) and Linear Discriminant Analysis (LDA), were applied to manage spectral complexity and highlight the principal biochemical contributors to AD pathology. Several Raman bands showed increased intensity in AD samples, such as 445 cm⁻¹ (N–C–S/C–C skeletal modes), 481 cm⁻¹ (DNA phosphate stretching), 560 cm-1 (Glycogen, tyrosine); 690 -780 cm-1 (Nucleic Acids); 748 cm⁻¹ (DNA bending), 1080 cm-1 (DNA symmetric stretching vibrations in Phosphate bonds (PO)4-2); 1554 cm⁻¹ (Amide II), and 1585 cm⁻¹ (protein‑folding–related vibrations) and 1607 cm-1 (Aromatic Amino acids- Phenylalanine/tyrosine; Cell Senescence - necrosis marker). These increases indicate enhanced protein aggregation, nucleic‑acid structural changes, and backbone reorganization. Conversely, multiple bands decreased in AD tissue, including 880 cm⁻¹ (tryptophan deformation), 951–952 cm⁻¹ (CH₃ vibrations of α‑helical proteins), 1000 cm⁻¹ (phenylalanine), 1296 cm⁻¹ (lipid CH₂ deformation), 1440 cm⁻¹ (lipid/cholesterol deformation), 1640–1680 cm⁻¹ (Amide I), and 1732 cm⁻¹ (C=O stretching). These reductions reflect loss of ordered protein secondary structure, disruption of aromatic amino‑acid environments, and extensive lipid membrane disorganization. Complementary gene‑expression analysis further demonstrated dysregulation of lipid homeostasis in AD, with altered expression of ABCA1, LIPE, CPT1A, PPARA, and SREBP‑1, indicating broad metabolic reprogramming. Together, the coordinated spectral and transcriptional shifts underscore lipid‑metabolic dysfunction as a central feature of AD. By capturing these molecular signatures, RS provides a promising tool for early detection and monitoring of AD progression.