Publication | Closed Access
Homocysteine and Oxidized Low Density Lipoprotein Enhance Platelet Adhesion to Endothelial Cells under Flow Conditions: Distinct Mechanisms of Thrombogenic Modulation
83
Citations
0
References
2000
Year
Distinct MechanismsVascular DiseaseEndothelial CellsImmunologyBiomedical EngineeringInflammationThrombosisHematologyPlatelet AdhesionCardiovascular Disease PathogenesisAtherosclerosisLow Density LipoproteinMolecular SignalingEndothelial Cell PathobiologyVascular BiologyPharmacologyThrombopoiesisCardiovascular DiseaseBlood PlateletEndothelial DysfunctionHemostasisFlow ConditionsMedicine
Summary We investigated the effects of two well established risk factors for cardiovascular disease, homocysteine and oxidized low density lipoprotein (ox-LDL), on endothelial cell thrombogenicity. For this purpose we studied platelet adhesion to human endothelial cells (EC) under flow conditions at a shear rate of 350 s−1 following EC treatment with either homocysteine or ox-LDL. Treatment of EC with either homocysteine (1 or 10 mmol/L for 16 h) or ox-LDL (100 µg/ml for 16 h) resulted in a 2-3 fold enhancement in platelet adhesion. The enhancement in platelet adhesion induced by 1 mmol/L homocysteine, but not that induced by 10 mmol/L homocysteine, was absolutely dependent on fibrin formation. Homocysteine treatment has significantly increased the cell surface tissue factor (TF) activity and slightly reduced the expression of the intercellular adhesion molecule I (ICAM-1). In contrast, ox-LDL treatment upregulated ICAM-1 expression and had no significant effect on endothelial TF activity. Neither homocysteine nor Ox-LDL affected surface expression of the αvβ3 integrin. The homocysteine-induced enhancement in platelet adhesion was almost completely abolished by blockade of the EC TF activity by a polyclonal antibody. The enhancing effect of homocysteine was also greatly reduced by inhibition of the EC αvβ3 integrin, but was not affected by blockade of EC ICAM-1. On the other hand, ox-LDL-induced enhancement in platelet – EC adhesion was greatly inhibited by blocking ICAM-1 or αvβ3, but remained unaffected by inhibition of TF activity. Preincubation of platelets with the glycoprotein IIb-IIIa (GPIIb-IIIa) antagonist Reo-Pro has virtually abolished the enhancing effect of both homocysteine and ox-LDL. Our results suggest that homocysteine and ox-LDL might increase endothelial thrombogenicity by distinct mechanisms: homocysteine – by inducing TF activity, and ox-LDL – by upregulating ICAM-1, both of which enhance GPIIb-IIIa/fibrinogen dependent platelet adhesion to EC. The αvβ3 integrin, although not affected by EC stimulation, seems to play a crucial role in platelet-EC interaction regardless of the mechanism of EC perturbation.