A carbon-13 NMR study of aortic lesions and cholesteryl ester rich lipoproteins from atherosclerotic rabbits

Abstract

When rabbits are fed a diet supplemented with cholesterol, their plasma cholesterol levels increased markedly and they developed atherosclerosis. Most of the plasma cholesterol exists as cholesteryl esters in very low density and low-density lipoproteins. Carbon-13 nuclear magnetic resonance (13C NMR) spectra (at 48 "C) of lipoproteins, and of arterial lesions from cholesterol-fed rabbits, are dominated by well-resolved cholesteryl ester resonances. An analysis of their line widths shows that the cholesteryl esters are in a liquid state at this temperature. Calculations based on line widths and spin-lattice relaxation times show that the motion of the cholesteryl ester molecules is highly anisotropic; motion about the long axis of the cholesteryl moiety is 38-75 times faster than motion about the short axis. Spectra for the lipoproteins and arterial lesions show temperature-dependent line-width

Quantification of Cholesteryl Esters in Human and Rabbit Atherosclerotic Plaques by Magic-Angle Spinning 13 C-NMR

“…This indicates that most of the CEs in the plaques used for this study were liquid at or near body temperature. These results agree with the previous NMR studies that show rabbit aorta plaque CEs were either in a liquid phase 25 or that liquid and liquid-crystalline phases coexisted near body temperature. 29 …”

“…Peak assignments were based on previous studies. 19,25,26 Because the T 1 values for C5 and C6 carbons in noncrystalline CEs are Ͻ1 second, 25 a 5-second pulse interval time was used to allow full magnetization relaxation, which is important for quantification studies at NMR intensity. The sample temperature was controlled within 1°C by the Bruker B-VT-1000 variable temperature unit.…”

“…The resonances of the C5 and C6 carbons in the sterol ring are well separated from the resonances of other components in plaques, including resonances of cholesterol. 16,25 The chemical shifts of the C5 and C6 resonances of CE are independent of acyl chain composition 22 and potentially suitable for quantification of total CEs in plaques. The inserts in Figure 2A show increasing intensities of the C5 and C6 peaks with increasing amounts of CEs.…”

13C-NMR spectroscopy of human atherosclerotic lesions. Relation between fatty acid saturation, cholesteryl ester content, and luminal obstruction.

“…13 The rupture of atheromatous plaques is a major contributor to the development of myocardial infarction, and it has been demonstrated that plaque vulnerability is dependent on the biochemical characteristics of the lipid pool. 47 Natural-abundance u C-nuclear magnetic resonance (NMR) spectroscopy allows the nondestructive characterization of lipid chemical composition.…”

“…47 Natural-abundance u C-nuclear magnetic resonance (NMR) spectroscopy allows the nondestructive characterization of lipid chemical composition. Because of its broad chemical shift bandwidth, 13 C-NMR provides more information regarding chemical constituents than 'H-NMR 810 and has been used for structural and dynamic studies of cholesteryl esters (CE), triglycerides (TG), and phospholipids (PL). "- 14 Hamilton and Cordes 15 examined plasma lipoproteins and intact ath-erosclerotic plaques in humans, demonstrating that atheroma had spectral characteristics very similar to those of thermally denatured LDLs, suggesting a comparable chemical composition.…”