In situ characterization of beta-amyloid in Alzheimer's diseased tissue by synchrotron Fourier transform infrared microspectroscopy

Abstract

We report the first evidence of the structure of beta-amyloid protein as it exists in situ within a slice of human Alzheimer's diseased brain tissue. Using a Fourier transform infrared microspectroscopic technique, areas of interest can be selected for spectral measurements with regions of potential contamination masked. In so doing, it is possible to obtain infrared spectra only of beta-amyloid and not the surrounding grey matter within which it lies. However, to obtain spectra of high-quality signal-to-noise ratio using a conventional infrared source, we were limited to aperture sizes between 24 microns x 24 microns to 50 microns x 50 microns. Markedly improved high-quality spectra were acquired with infrared radiation provided by a synchrotron light source (National Synchrotron Light Source, Brookhaven National Laboratories), using aperture sizes as small as 12 microns x 12 microns. This allowed spectroscopic mapping of brain tissue regions containing amyloid. We observe that in situ protein of grey matter exist predominantly in an alpha-helical and/or unordered conformation, whereas within amyloid deposits a beta-sheet structure predominates. The hydrogen bonding strength of the beta-structure found in situ is different from that reported in the literature for isolated/chemically synthesized beta-amyloid peptides.

Beta-amyloid deposition and Alzheimer's type changes induced by Borrelia spirochetes

“…Characteristic absorption bands observed in many biological materials include the 'Amide I' band at 1650 cm −1 resulting largely from the number of carbonyl (C O) stretching vibrations of protein amide bonds. A second peak in the "Amide I" band near 1630 cm −1 , is present in senile plaques representative of ␤-sheet protein structure [6]. This peak near 1630 cm −1 was observed not only in the senile plaques of the 5 AD cases tested, but also in the thioflavin S-positive "plaques" in infected cell cultures following 4-week exposure to Borrelia.…”

“…The infrared absorption microspectrum of healthy brain tissue exhibits a protein (Amide I) absorbance maximum near 1655 cm −1 , representative of an average ␣-helical protein structure in the tissue [6]. SIMRS analysis detected a second peak near 1630 cm −1 in senile plaques in AD, representative of ␤-sheet protein structure.…”

“…A Spectra Tech Continu m infrared microscope coupled to a Nicolet Magna 860 FTIR was used, where the conventional infrared source was replaced by synchrotron light from Beamline U10B (National Synchrotron Light Source, Brookhaven National Laboratory). The infrared microscope was equipped with a light source and filters for fluorescence microscopy analysis [6,7]. For the SIRMS analysis, infected and uninfected cells were harvested by centrifugation, washed with PBS, placed on infrared-transparent BaF 2 slides and stained with thioflavin S. Samples of infected and uninfected astrocyte cultures derived from three different experiments at 4-week exposure times were analyzed.…”

A novel fuzzy clustering algorithm for the analysis of axillary lymph node tissue sections

“…Reference (5), dist min (0.0006) is not smaller than or equal to 1/2 rest of dist (0.00045); meantime, it does not satisfy the second condition either. Hence, in this situation, no merging conditions are satisfied, and so the iteration stops as defined in (6).…”

“…These problems in diagnosis have led to considerable interest in investigating the application of spectroscopic approaches for disease diagnosis [1,2]. Fourier transform infrared (FTIR) spectroscopic imaging provides a chemical fingerprint of microscopic areas within a tissue sample [3][4][5][6]. Contrast between different spatial areas of a sample is due to the chemical differences that are occurring within the cells of the tissue.…”