Identification of Different Lipid Phases and Calcium Phosphate Deposits in Human Carotid Artery Plaques by MAS NMR Spectroscopy

Accumulation of lipids in atherosclerotic plaques causes progressive narrowing of the arterial lumen, often followed by thrombosis and ischemia. Currently several different methods, most requiring disruption of the plaque, are used to study the physical properties of lipids accumulated in plaques, and lipid composition is typically determined by chemical analysis of completely disrupted plaques. In this study, 13C magic angle spinning NMR spectroscopy (MAS NMR) was used to determine in situ the lipid composition and molecular organization of all lipid phases in human carotid artery plaques (ex vivo). Protocols were developed to observe signals from one lipid phase without interference from other phases. In addition, 31P MAS NMR detected calcification in plaques by the signals from inorganic phosphate complexed to calcium. Together, 13C and 31P MAS NMR comprise a powerful nondisruptive approach for determining the quantity and phase state of components in arterial plaques.