Abstract
In aortic stenosis plasma lipoprotein-derived lipids accumulate in aortic valves. Here, we first compared the lipid compositions of stenotic aortic valves and atherosclerotic plaque cores. Both pathological tissues were found to be enriched in cholesteryl linoleate, a marker of extracellularly accumulated lipoproteins. In addition, a large proportion of the phospholipids were found to contain arachidonic acid, the common precursor of a number of proinflammatory lipid mediators. Next, we isolated and characterized extracellular lipid particles from human stenotic and non-stenotic control valves, and compared them to plasma lipoproteins from the same subjects. The extracellular valvular lipid particles were isolated from 15 stenotic and 14 non-stenotic aortic valves. Significantly more apoB-100-containing lipid particles were found in the stenotic than in the non-stenotic valves. The majority of the lipid particles isolated from the non-stenotic valves had sizes (23±6.2 nm in diameter) similar to those of plasma low density lipoprotein (LDL) (22±1.5 nm), while the lipid particles from stenotic valves were not of uniform size, their sizes ranging from 18 to more than 500 nm. The lipid particles showed signs of oxidative modifications, and when compared to isolated plasma LDL particles, the lipid particles isolated from the stenotic valves had a higher sphingomyelin/phosphatidylcholine –ratio, and also higher contents of lysophosphatidylcholine and unesterified cholesterol. The findings of the present study reveal, for the first time, that in stenotic human aortic valves, infiltrated plasma lipoproteins have undergone oxidative and lipolytic modifications, and become fused and aggregated. The generated large lipid particles may contribute to the pathogenesis of human aortic stenosis.
Highlights
The non-rheumatic calcific aortic valve disease, or aortic stenosis (AS), is an active fibrocalcific condition of the aortic valves, and it develops gradually over decades before becoming clinically manifested [1]
Lipids were extracted from 6 stenotic valve leaflets (Table 1, subjects R-X) and from the cores of 3 atherosclerotic plaques, after which their lipid compositions were analyzed by electrospray ionization-mass spectrometry (ESI-MS)
We found that in the whole stenotic aortic valves and in the atherosclerotic plaque cores, the 18:1/[18:1+18:2] ratios were, on average 0.19 (60.05; median 0.19) and 0.22 (60.01; median 0.23), respectively, a finding indicating that the accumulated lipids in both tissues were mainly of extracellular origin
Summary
The non-rheumatic calcific aortic valve disease, or aortic stenosis (AS), is an active fibrocalcific condition of the aortic valves, and it develops gradually over decades before becoming clinically manifested [1]. The lesions in aortic valves emerge subendothelially on the aortic side of the valvular leaflets, where the endothelial cells most likely get damaged as a result of severe shear stress, the dysfunctional endothelium providing access for plasma lipoproteins and leukocytes to the subendothelial fibrosa layer [7,8]. This subendothelial layer contains a proteoglycan-rich extracellular matrix [9], i.e. a matrix offering a suitable ground for lipoprotein retention [10,11]. In aortic valves, apoB-100 has been detected already in early stages of the disease development and its amount increases with the progression of the disease [12,13]
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