Interactions of a covalently - linked antithrombin-heparin complex with components of the fibrinolytic pathway

Abstract

<p>Unfractionated heparin (UFH) is used as an adjunct during thrombolytic therapy. However, its use is associated with many clinical limitations, such as the inability to inhibit fibrin-bound coagulation factors, increasing the potential for sustained procoagulant activity. We have developed a covalent conjugate of antithrombin (AT) and heparin (ATH) with superior anticoagulant properties to those of UFH. Some advantages of ATH include enhanced inhibition of surface-bound enzymes and its ability to reduce the overall size and mass of clots <em>in vivo</em>. However, the potential interactions of UFH or ATH with the components of the fibrinolytic pathway are not well understood. Therefore, our study utilized discontinuous second order rate constant (<em>k₂</em>) assays to determine rates of inhibition of plasmin (Pn) in the presence or absence of fibrin by AT+UFH <em>vs.</em> ATH. In addition, we monitored the rates of Pn generation in a system comprised of preformed fibrin clots with the aim of evaluating the inhibitory effect of AT+UFH or ATH in this more native system. The <em>k₂</em>values for the inhibition of Pn without fibrin were 5.74x10⁶±0.278x10⁶ and 6.39x10⁶±0.588x10⁶ for AT+UFH and ATH, respectively (p=0.36). In the presence of fibrin, the <em>k₂</em>values decreased to 1.45x10⁶±0.0971x10⁶ for AT+UFH and 3.07x10⁶±0.192x10⁶for ATH (<em>p</em></p>