Homocysteine and oxidized low density lipoprotein enhanced platelet adhesion to endothelial cells under flow conditions: distinct mechanisms of thrombogenic modulation.
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 microg/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 alpha(v)beta3 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 alpha(v)beta3 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 alpha(v)beta3, 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 alpha(v)beta3 integrin, although not affected by EC stimulation, seems to play a crucial role in platelet-EC interaction regardless of the mechanism of EC perturbation.
Dardik
R
R
National Hemophilla Center and Institute of Thrombosis and Hemostasis, Sheba Medical Center, Tel Hashomer, Israel.
Varon
D
D
Tamarin
I
I
Zivelin
A
A
Salomon
O
O
Shenkman
B
B
Savion
N
N
D000077284:Abciximab; D000906:Antibodies / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D015815:Cell Adhesion Molecules / Q000096:biosynthesis / Q000187:drug effects; D004730:Endothelium, Vascular / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D005337:Fibrin / Q000096:biosynthesis / Q000502:physiology; D005340:Fibrinogen / Q000494:pharmacology; D006710:Homocysteine / Q000494:pharmacology* / Q000502:physiology; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D018799:Intercellular Adhesion Molecule-1 / Q000096:biosynthesis / Q000187:drug effects; D008077:Lipoproteins, LDL / Q000494:pharmacology* / Q000502:physiology; D010084:Oxidation-Reduction; D010973:Platelet Adhesiveness / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000187:drug effects; D019030:Receptors, Vitronectin / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism; D013925:Thromboplastin / Q000096:biosynthesis / Q000187:drug effects / Q000276:immunology; D014471:Umbilical Veins / Q000166:cytology
D000906:Antibodies; D000911:Antibodies, Monoclonal; D015815:Cell Adhesion Molecules; D007140:Immunoglobulin Fab Fragments; D008077:Lipoproteins, LDL; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011956:Receptors, Cell Surface; D019030:Receptors, Vitronectin; C099252:oxidized low density lipoprotein; D006710:Homocysteine; D018799:Intercellular Adhesion Molecule-1; D005337:Fibrin; D005340:Fibrinogen; D013925:Thromboplastin; D002118:Calcium; D000077284:Abciximab