Chemical analysis of multiple sclerosis lesions by FT-IR microspectroscopy

Fourier transform infrared microspectroscopy can be used to collect infrared spectra from microscopic regions of tissue sections. If spectra are collected along a grid pattern, then maps of chemical functional groups can be produced and correlated to tissue histopathology. In the present study, white matter from multiple sclerosis and control brains were examined. Mapping experiments were designed such that 17 spectra were collected at 200 microm intervals along a line that was partially or wholly within a multiple sclerosis lesion site or within a representative white matter region of control tissue. Data analysis was based on earlier in vitro studies which found that the carbonyl at 1740 cm(-1) increases when lipids become oxidized (Free Rad. Biol. Med. 16:591-601, 1994), and the amide I peak at approximately 1660 cm(-1) broadens when proteins become oxidized (FEBS Let. 362:165-170, 1995). The results indicated that the C=O to CH2 ratio (1740 cm(-1):1468 cm(-1)) was elevated at several collection points in lesion sites from multiple sclerosis brains compared to values from white matter of control brains. Inspection of the amide I peak at 1657 cm(-1) revealed that it was broadened towards 1652 cm(-1) in multiple sclerosis tissues but not control tissues. These results suggest that lipids and proteins could be oxidized at active multiple sclerosis lesion sites. The localization of these products to lesion sites supports a role for free radicals in the pathogenesis of multiple sclerosis.