One of the hallmarks of
atherosclerosis is the accumulation of
lipoproteins within the wall of blood vessels. The
lipid composition can vary among
atheroma, even within a single individual, and is also dynamic, changing as the lesion progresses. One desirable characteristic of
atheroma is their stability, as the
rupture of unstable plaques can interfere with normal blood flow to the brain or heart, leading to
stroke or
heart attack. Desorption electrospray ionization mass spectrometry (DESI-MS) was used in this study for the profiling and imaging of arterial plaques. DESI-MS is an ambient ionization method in which a charged, nebulized
solvent spray is directed a surface. In the positive and negative ion modes,
sodium and
chloride adducts, respectively, of diacyl glycerophosphocholines (GPChos),
sphingomyelins (SMs), and hydrolyzed GPChos were detected. Also,
cholesteryl esters were detected via adduct formation with
ammonium cations. Finally,
cholesterol was imaged in the
atheroma by doping the charge labeling
reagent betaine aldehyde directly into the DESI
solvent spray, leading to in situ chemical derivatization of the otherwise nonionic
cholesterol. DESI imaging experiments, in which the spatial distribution of the various chemical species is determined by scanning the DESI probe across an entire sample surface, revealed that there are
lipid rich regions within the arterial walls, and the
lipid rich regions seem to have one of two different
lipid profiles. These
lipid rich regions likely correspond to the areas of the tissue where
lipoprotein particles have accumulated. It is also possible that the different
lipid distributions may correlate with the stability or vulnerability of that particular region of the plaque.