Infrared Micro-imaging of Atherosclerotic Arteries

Micro-FT-IR spectroscopy is a versatile technique that enables the user to obtain high-quality spectra on small samples. This technique is employed to probe the subcellular chemical composition of atherosclerotic arterial walls and create three-dimensional images representing changes in the composition. Two different rabbit model systems that produced atherosclerosis, either due to genetic disorder or due to physical injury, are studied. The FT-IR spectra are collected from a 20- × 20-μm area of 5-μm-thick arterial section, which is smaller than a single cell. The presence of cholesterol esters and other ester-containing compounds is identified from the -O-C=O stretching (1735 cm−1) absorption, and the cis unsaturation in the acyl chains of these compounds is represented by C=C-H stretching (3005 cm−1) absorption. The protein content is indicated by the intensities of the amide I (1650 cm−1) band. The data clearly show the changes occurring in the chemical composition of an arterial wall, varying with the physiological and morphological changes within the artery and the arteries from different animal models. The power of this technique is demonstrated by excellent correlation with the hot stage polarizing microscopy technique, used to characterize the arterial lipids in situ. The three-dimensional images of the arterial walls, indicating the concentration of different chemical constituents, are very useful in understanding the mechanism of atherosclerosis development.