Inhibition of Plasmin Generation in Plasma by Heparin, Low Molecular Weight Heparin and a Covalent Antithrombin-Heparin Complex (ATH)

Abstract

Unfractionated heparin (UFH) and low molecular weight heparin (LMWH) are commonly used anticoagulants to treat thrombotic diseases. However, these anticoagulants are associated with some limitations such as increased bleeding, variable dose response, and the necessity for frequent monitoring. This led to the development of the antithrombin-heparin covalent complex (ATH) which has been shown to overcome many of these limitations. Numerous past studies have proven ATH to be a better anticoagulant in comparison to UFH. More recent studies aimed at studying its interaction with the fibrinolytic pathway. It was observed that ATH inhibited free and fibrin bound plasmin (Pn), the main serine protease of fibrinolysis. As well, the rates of Pn generation on fibrin clots decreased in the presence of ATH. These studies were conducted in purified systems and did not elucidate the interaction of ATH with Pn in the presence of its natural inhibitors, α2-macroglobulin (α2-M) and α2-antiplasmin (α2-AP). Thus, this study focuses on analyzing the effects of ATH in comparison to UFH and LMWH on Pn generation in plasma, to allow for a better understanding of such mechanisms under more physiological conditions. In comparison to the absence of anticoagulants, total Pn generated decreased in the presence of 0.7 U/ml of UFH or ATH and 2.1 U/ml of ATH. This confirms previous in vitro studies in which UFH + AT and ATH can inhibit Pn activity. In addition, quantified Pn bound α2-M complexes showed a reduction at 0.7 U/ml of ATH suggesting that ATH may be able to compete with α2-M for Pn. However, the amount of quantified Pn bound α2-AP complexes were not affected as α2-AP is a much faster inhibitor of Pn. It was noted that LMWH did not affect Pn generation. As a result, this study adds to our understanding of ATH mechanisms of action and aids in its development for clinical use.