Infrared spectroscopic investigation of control and diseased central nervous system tissue: A multidisciplinary approach to tissue characterization

The application of infrared (IR) spectroscopy to the investigation of biological molecules has, to date, primarily focused upon the analysis of isolated biomolecules as a result of the general consensus that the infrared spectra of whole tissue systems would be too complicated to decipher. Herein, I present evidence of the novel biomedical application of IR spectroscopy for the analysis of complex tissue assemblies. Based upon the premise that IR spectroscopy is known to be a sensitive biophysical technique capable of yielding molecular information concerning the structure and composition of isolated biomolecules, we have used this technique for the characterization of control and diseased human central nervous system tissue (CNS). We propose that the biochemical changes occurring within cells and tissues in disease should be detectable by alterations in the infrared spectra.; Our infrared spectroscopic analysis of autopsy human CNS tissue revealed that the spectra of control grey matter and control white matter can be readily distinguished by marked differences in spectral absorptions arising from lipids components. White matter spectra are dominated by lipid absorptions whereas grey matter spectra demonstrate reduced lipid absorptions compared to white matter. We next investigated diseased CNS tissue for spectral signatures characteristic of neurodegeneration and demyelination. Using FTIR synchrotron microspectroscopy, we have spectroscopically mapped regions or Alzheimer's diseased (AD) tissue, and determined the presence and protein secondary structure of extracellular amyloid deposition and amyloid angiopathy in the AD brain. We observe that in-situ, proteins of grey matter exist predominantly in an {dollar}alpha{dollar}-helical and/or unordered conformation, whereas within amyloid deposits, a {dollar}beta{dollar}-sheet structure predominates. The hydrogen bonding strength of {dollar}beta{dollar}-structure found in-situ is different from that reported in the literature for isolated/chemically synthesized {dollar}beta{dollar}-amyloid peptide.; Our spectral analysis of multiple sclerosis (MS) plaque tissue revealed characteristic decreases in lipid absorptions compared to spectra of control white matter. These changes are the result of lipid loss in demyelination. Furthermore, we observed evidence of the underlying biochemical differences between chronic and acute MS plaques. Spectra of acute demyelinating plaques exhibit infrared absorptions indicative of protein breakdown products and the increased presence of cholesteryl esters. In contrast, spectra of chronic MS plaques displayed absorptions which are attributed to the accumulation of glial fibrillary acidic protein in CNS scar tissue. Lastly, near-infrared spectroscopy coupled with fibre optic probes was used to assess demyelination and remyelination in an animal model, and to demonstrate the potential of using this technique for the non-invasive characterization of disease changes in the brain.; This thesis research has involved a novel multidisciplinary approach to tissue characterization, drawing on the wealth of knowledge in the fields of neuropathology, biochemistry and IR spectroscopy. We have demonstrated that the infrared spectroscopic investigation of complex tissue assemblies enhances our understanding of the molecular alterations occurring in disease processes. It is hoped that these studies will lay the foundation for future studies aimed at developing non-invasive IR diagnostic methods for disease detection.