Structural features and bleeding activity of commercial low molecular weight heparins: neutralization by ATP and protamine.

Differences in the structure of three low molecular weight heparins (LMWHs) have been observed by applying physico-chemical methods as well as enzymatic degradation with bacterial heparinase and heparitinase II. The production of enoxaparin maintains the internal structure of the parent heparin with the exception of the unsaturated nonreducing end. In contrast, the production of dalteparin and nadroparin removes part of their nonsulfated uronic acid residues and, unlike enoxaparin and unfractionated heparin (UFH), these LMWHs also contain regions that remain resistant to the action of heparitinase II. Enoxaparin has a lower molecular weight distribution than dalteparin and nadroparin and is composed of at least four discrete molecular weight populations. A rat-tail model demonstrated that LMWHs applied topically or injected intravenously had a lower bleeding potency when compared with UFH treatment. The bleeding potencies of the different LMWHs were similar. Furthermore, adenosine triphosphate (ATP) completely neutralized bleeding caused by LMWHs and UFH in the animal model when applied topically and significantly reduced bleeding in heparinized surgical patients undergoing cardiopulmonary bypass surgery.