Spatial Distributions of Lipids in Atherosclerosis of Human Coronary Arteries Studied by Time-of-flight Secondary Ion Mass Spectrometry

The accurate spatial distribution of various lipid species during atherogenesis has remained unexplored. Herein, we used time-of-flight secondary ion mass spectrometry (TOF-SIMS) to analyze the lipid distribution in human coronary artery cryosections. The images from the TOF-SIMS allowed visualization of ions derived from individual species of cholesterol esters, phospholipids, and triacylglycerols in the context of lesion characteristics and severity. In addition, cholesterol-containing crystal-like structures were seen in high-resolution images of advanced lesions. The ratio of cholesterol fragment ions (m/z 385:m/z 369) was found to differentiate unesterified cholesterol from cholesterol esters. This ratio changed during atherogenesis and in different areas of the lesions, reflecting differences in the accumulation of the two forms of cholesterol. Thus, atheromas were characterized by accumulation of cholesterol esters with apolipoprotein B near the intima-media border, whereas in the complicated lesions, unesterified cholesterol dominated in neovessel-containing areas enriched in glycophorin A. Interestingly, triacylglycerols were found in areas surrounding neovessels and lacking either form of cholesterol. The lipid composition of the tunica media reflected the alterations observed in the intimal lipids, yet being more subtle. The detailed molecular information obtained by TOF-SIMS revealed unanticipated differences in the type and composition of the accumulating lipids in different stages of atherogenesis, notably the spatial segregation of cholesterol and triglycerides in the advancing lesions.