Infrared Spectroscopy of Lipoproteins: A Comparative Study of Normal and Diabetic Plasma Lipoproteins

Abstract

Infrared spectroscopy has been applied to study the composition and secondary structures of very low-density (VLDL), low-density (LDL), and high-density (HDL) plasma lipoproteins from diabetic and nondiabetic control rats. Both nondiabetic and diabetic lipoproteins generate spectra characterized by distinct amide I band spectral profiles, which were fitted to a sum of component bands diagnostic for types of protein secondary structure. From the spectra of both diabetic and healthy rat groups we find the following results: (1) although the esterified lipid/apoprotein ratio is conserved in both groups of HDL, LDL, and VLDL lipoproteins, healthy LDL particles seem to be richer in phospholipids than diabetic LDL; (2) this different lipid composition is accompanied by a lower β-sheet proportion in diabetic LDL lipoproteins; (3) The percentage area corresponding to tyrosine residue is higher in healthy HDL and LDL lipoproteins compared with the diabetic ones. The reverse occurs for VLDL lipoproteins, which indicates either an apoprotein composition change or an apoprotein transfer from HDL and LDL to VLDL particles during the diabetic process. All the above changes in lipid and apoprotein composition as well as protein conformational changes during diabetes disease can result in a decreased binding of apoproteins to the cellular LDL receptor.