Low density lipoprotein binding to human platelets: role of charge and of specific amino acids.
ABSTRACT Many human and animal cells possess cell surface binding sites, specific for low density lipoproteins. Human platelets are similarly endowed with specific low density lipoprotein receptors. Using chemical modofications of amino acid residues on the low density lipoprotein molecule, we have studied the role of charge and specific amino acids on the binding process. The interaction of the modified low density lipoprotein preparations with gel-filtered platelets and with glass beads was compared. Both cyclohexanedione treated and aceto-acetylated low density lipoprotein did not bind to the platelet surface. However, azo-arsanilated low density lipoprotein bound to the platelets in a manner similar to the binding of native lipoprotein. Cyclohexanedione treated lipoprotein was the only preparation which did not bind to glass beads. The importance of both the presence of the positive charge on the lipoprotein molecule and the availability of specific amino acid residues (arginine and lysine but not tyrosine and histidine) for low density lipoprotein-platelet interaction was thus demonstrated.
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ABSTRACT: The effects of chronic uraemia and serial acetate (HDA) or bicarbonate (HDB) hacmodialysis on the aggregation, thromboxane B2 (TXB2) release and cyclic AMP (cAMP) concentration of platelets from arterial blood were studied in 14 uraemic patients (6 dialysed and 8 conservatively treated) and 10 controls. Platelets from uraemic patients, either dialysed or treated conservatively, exhibited a significantly higher cAMP level (P2 level (PPPP2 formation were observed after HDB than after HDA. The concentration of platelet cAMP and aggregability, and also the platelet cAMP and the TXB2 level showed a significantly negative correlation (r=-0.7,Pr=-0.60,P2 and the aggregability (r=0.67,P2 or aggregation results. The dysfunction of uraemic platelets accompanied by a reduced TXB2 release may be explained by an increased cAMP and a decreased arachidonic acid availability. HDB improves the platelet function to a greater degree than does HDA.Pediatric Nephrology 01/1991; 5(3):327-331. · 2.94 Impact Factor
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ABSTRACT: We present evidence of a link between low-density lipoprotein (LDL) receptor binding and activation of a platelet G-coupled protein. LDL stimulation induced cytosolic [Ca2+]i mobilization, increase in inositol 1,4,5-triphosphate (IP3) formation and a rapid cytosol-to-membrane translocation of protein kinase C (PKC) enzymatic activity. Pertussis toxin inhibited all the stimulatory effects, whereas cholera toxin had no effect. Using ligand-binding assays, we demonstrated that exposing platelet LDL receptors to high concentrations of LDL (1.5 g/l) caused a rapid down-regulation and desensitization, as shown by the reduction in the Bmax, intracellular [Ca2+]i mobilization and IP3 formation to 65, 73 and 63%, respectively. The inhibitory effects were reversible and dose and time dependent. Furthermore, VLDL (0.2 g/l) and IDL (0.07 g/l) induced similar desensitization effects. However, HDL3 (up to 1.5 g/l), chylomicrons (up to 0.5 g/l) and cyclohexandione-modified LDL (which does not bind to platelets) had no significant effects. Protein kinase C inhibitors (150 nmol/l staurosporine, 100 μmol/l H-7, and 10 nmol/l bisindolylmaleimide) inhibited desensitization to 71%, on average. Sequestration blocking agents (0.30 g/l, concanavalin A) had no significant effect if phosphorylation was operative. However, there was a complete blockade with the concurrent inhibition of both pathways. In contrast, cAMP-dependent protein kinase inhibitors (PKI, 1 μmol/l) or β2-adrenergic receptor kinase inhibitors (100 nmol/l, heparin), had no effect. Overall results indicate that LDL binds to a pertussis sensitive G-protein coupled receptor and that high levels of lipoproteins down-regulate the number of receptors and desensitize its mediated response by a mechanism that involves PKC-phosphorylation and sequestration of binding sites. This new regulatory mechanism may have implications for the thrombogenicity in hyperlipidemia and for effects of lipid lowering therapy.Atherosclerosis 01/2001; 155(1):99-112. · 3.71 Impact Factor
- Doklady Biological Sciences 11/2013; 453(1):333-5.