The effects of low density lipoproteins modified by incubation with chondroitin 6-sulfate on human aortic smooth muscle cells

One of the first changes that take place within the artery intima at the in ception of atherosclerosis is the accumulation of LDL-derived modified lipo proteins which appear as subendothelial lipid droplets and vesicles. With t ime, the LDL retention and interaction with intimal chondroitin sulfate-pro teoglycans may induce further structural and functional modification of the lipoproteins. The aim of this study was to produce 'in vitro' modified lip oproteins by LDL incubation with chondroitin 6-sulfate (CS, at 37 degrees C , for 48 h, in the absence of antioxidants-) and to test their effects on c ultured human aortic smooth muscle cells (SMCs). CS induced LDL modificatio n (CS-mLDL) consisted in formation of a mixture of fused particles (up to 1 50 nm diameter) and monomers with a small content of lipid peroxides and a partially degraded apo B-100, corresponding to a mild oxidation. Upon incub ation with SMCs, CS-mLDL produced a concentration-dependent stimulation of H-3-thymidine incorporation, that, at low concentration (25 mu g/ml), was 2 -3-fold higher than that obtained when native LDL was used; this increase c orrelates well with the level of CS-mLDL uptake at the same concentration. Besides the mitogenic effect, CS-mLDL induced a significant stimulation of SMCs migration, comparable with that reported for oxidized LDL. Upon incuba tion with CS-mLDL, SMCs accumulated lipid droplets of various number and di mension, as revealed by Nile red staining and electron microscopy. Competit ion studies performed in the presence of 20-fold excess of native LDL and a cetyl LDL showed that I-125-CS-mLDL were taken up both by LDL receptor and scavenger receptor. At high concentration (200 mu g/ml), CS-mLDL had a cyto toxic effect that was not significantly different from that of native LDL. Together these results provide evidence of (i) the direct alteration produc ed by CS on LDL and (ii) the effect of CS-mLDL on SMCs migration, prolifera tion and transformation in lipid-laden cells, events that are crucial in th e development of fibro-muscular atherosclerotic lesions. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.