An infrared spectroscopic study of aortic valve. A possible mechanism of calcification and the role of magnesium salts.

In the present study fourier transform infrared (FT-IR) spectroscopy was used to study the mechanism of pathogenesis of aortic valve calcification. The high intensity bands of vCH3 and vCH2 groups of lipids and phospholipids of membranes, in the spectral region 3000-2800 cm(-1), show the high concentration of lipids and fatty components in aortic valve, resulting from degradation of the main aliphatic chain of the membranes, with a change of their permeability and fluidity. The presence of bands at 3075 and 1744 cm(-1), assigned to olefinic (v=CH) and aldehyde carbonyl groups, respectively, implies that reactive oxygen species are involved in the initiation of peroxidation of the lipids and phospholipids. These latter bands are related to the oxidative stress of the patients. From the shifts of bands to lower frequencies of the characteristic absorption bands of amide I and amide II, it is suggested that the proteins change their secondary structure from α-helix to β-sheets and random coil due to modifications of collagen, associated with the permeability of aortic valve atherosclerosis. From the spectral region 1150-900 cm(-1), where the characteristic stretching vibration bands of the phosphate groups (vPO4(-3)) absorb, the calcified aortic valve was found to contain biological hydroxyapatite (Ca10(PO4)6(OH)2), as well as amorphous hydroxyapatite (Ca5(PO4)xOH) and CaHPO4. These findings are in agreement with scanning electron microscopy energy-dispersive X-ray analysis and X-ray diffraction analyses. SEM micrographs show that the valves are rich in fibrils and that the protein-protein cross-linked chemical bonds seem to be the points of initiation of calcification.