Measurement of the Antithrombin III Binding Sites in Low Molecular Weight Heparins by 13C NMR and Capillary Electrophoresis

Abstract

Low molecular weight heparins, prepared from the controlled chemical or enzymatic depolymerization of the heparin polysaccharide, are currently replacing heparin as the clinical anticoagulant/antithrombotic agent of choice. A principal mechanism of action of these agents is through the binding of antithrombin III, a plasma serine protease inhibitor, to specific pentasaccharide sequences in these polysaccharides. The content of antithrombin III-binding pentasaccharide sequences within low molecular weight heparins vary, making these drugs bio-inequivalent. Currently, the only way to examine the content of these pentasaccharide sequences within a low molecular weight heparin preparation relies on bioassay. This study examined both 13C NMR spectroscopy and oligosaccharide analysis by capillary electrophoresis as alternative measures of the content of antithrombin III binding sites within a variety of low molecular weight heparins. The number of antithrombin III binding sites per chain, measured by 13C NMR spectroscopy, correlated with the antithrombin III mediated anti-factor Xa activity of various low molecular weight heparins.