Interaction of Immobilised Unfractionated and LMW Heparins with Proteins in Whole Human Plasma

Abstract

The profile of proteins bound to immobilised heparins in hirudin-anticoagulated human plasma was analysed. In molar terms, antithrombin III was the most abundant protein bound to therapeutic doses of unfractionated heparin (M(r) = 12,000), whereas heparin cofactor II constituted < 1% of the protein bound. Histidine-rich glycoprotein was the only plasma protein likely to influence anticoagulant activity by direct competition with antithrombin III, though significant quantities of complement Factor H, fibrinogen, fibronectin, vitronectin and apolipoprotein B were also detected. Only traces of von Willebrand factor, complement factor I, inter-alpha-trypsin inhibitor, alpha 2-macroglobulin, serum amyloid P and transferrin were identified, and neither thrombospondin nor platelet factor 4 were measurable. Binding of both antithrombin III and histidine-rich glycoprotein varied with the ratio of heparin to plasma. Clexane (M(r) = 4,500) also bound antithrombin III, but both histidine-rich glycoprotein and vitronectin were quantitatively significant neutralising proteins. Neutralising proteins dominated the binding profile for Oligo H (M(r) = 2,200).