Changes in elastin in human atherosclerotic aorta: carbon-13 magic angle sample-spinning NMR studies

The dipolar-decoupled, natural abundance Fourier transform and cross polarization [13C] NMR spectra of human elastin isolated from atherosclerotic aorta and aortas free of atherosclerotic lesions, bovine insoluble elastin and bovine kappa-elastin were obtained at 75 MHz, with 5-7 kHz magic angle sample spinning. Spin-lattice rotating frame relaxation parameters were measured for protons (T1pH) and for carbons (T1pC) at room temperature. Proton relaxation times were shorter for bovine kappa-elastin (T1pH = 1.7 ms) than for bovine elastin (T1pH) = 3.5 ms). Calculation of T1pH showed no differences between human normal and atherosclerotic elastins. T1pC were shorter for bovine kappa-elastin than for bovine elastin. While alpha-carbons of human atherosclerotic elastin had shorter T1pC than normal elastin alpha carbons, carbons from hydrophobic amino acid side chains had longer T1pC for atherosclerotic then for normal elastin. Biochemical studies of aortic wall and purified elastin showed significantly increased content of lipids (atherosclerotic 67.7 mmol/g elastin, control 54.7 mmol/g elastin) and calcium (atherosclerotic 38.3 mmol/g elastin, control 19.6 mmol/g elastin). Changes in relaxation parameter values may be caused by the structural and biochemical changes in human elastin. Increased mobility of polypeptide chains as based on the model kappa-elastin studies is caused by the action of elastase. Restriction of mobility is expected to be caused by the accumulation of lipids and calcium.