Effects of native and modified low density lipoproteins on functional and biochemical aspects of cells involved in the thrombotic process

Recent studies indicate that low density lipoproteins (LDL), either native and/or chemically and/ or cell modified LDL, interact with blood and vascular cells influencing specific functional and biochemical aspects that are of relevance in the onset of thrombotic processes. In vitro studies indicate that LDL may influence platelet reactivity in terms of both aggregation and thromboxane biosynthesis. In addition, chemically and/ or oxidized LDL have been shown to induce endothelial cell perturbation. In particular, both native and acetyl-LDL have been demonstrated to increase the synthesis and the re lease of the inhibitor of plasminogen activator type 1 (PAI-l) by human umbilical vein endothelial cells (HUVEC). The effect of both native and acetyl-LDL is concentration-dependent and is spec ific for this lipoprotein, since they do not influence either t-PA release or the expression of Tissue Factor activity (TFa) by the cells. In contrast, chemically oxidized LDL do not induce increases in PAI-l release by HUVEC, but, instead, they increase the expression of TFa thus enhancing the capacity of HUVEC to localize fibrin formation. It is of interest to note that the effect of lipoproteins on TF expression differs according to the cell type considered. In fact, in human monocytes the expression of TFa is enhanced by acetyl-LD L, whereas native and chemically oxidized LDL inhibit it.