The distribution and morphology of aortic valve cusp lipids

During dissections of porcine aortic valves, we noted clusters of spherical droplets, roughly 50 micrometers in size, within the central spongiosa of the valve cusps. Oil red-O staining of fresh tissues confirmed that the clusters were lipids, and thin layer chromatography showed that they consisted mainly of free cholesterol and triglycerides, with some cholesterol ester. The distribution of these clusters in 60 cusps from 20 porcine aortic valves was mapped using computerized morphometry. The ventricularis was peeled back to expose the spongiosa, and the spatial distribution of the lipid droplets was analyzed using a stereological point counting method. Computer averaging of lipid density images was done to obtain a mean distribution map of lipid occurrence. This distribution map suggests that porcine aortic valve lipids are found predominantly at the base of the valve cusps, and are conspicuously absent from the coaptation regions and the free edge. Moreover, 19/20 valves had lipids in the left coronary cusp and all 20 valves had lipids in at least two of the three cusps. Endogenous lipids are therefore ubiquitous in porcine aortic valves and may play a role in the calcification of xenograft bioprostheses.