Dementia is one of the main death leading causes worldwide and Alzheimer’s disease (AD) is its most common form. In postmortem examinations of AD brain tissue, extracellular deposits of proteins are observed, known as amyloid-beta (Aß) plaques. Aß plaques are characterized by their occurrence of beta-sheets and are, beside tau tangles, biological hallmarks in the postmortem diagnosis of AD. Little research on the detectability of Aß deposits in brain tissue using Raman spectroscopy has been published.
Here, we examined formalin fixed, paraffin embedded tissue slices of AD and healthy control cases. The slices have been spectrally raster imaged with a step size smaller the size of a plaque using a commercial Raman spectroscope with a NIR laser source to obtain a hyperspectral map of the size of 0.5mm2. Specific band intensities including, among others, protein and lipid components were analyzed and afterward compared to the healthy control cases to study spectral differences. Further, Aß deposit locations could be precisely matched to the obtained spectral data by staining the same Raman imaged tissue slice with Thioflavin afterward. In addition, plaques can be co-localized by using histochemical stained adjacent tissue slices.
In conclusion, we present new insights on spectral changes in the Raman fingerprint region of 950 to 1800cm-1 when analyzing the molecular composition of AD brain tissue.