Low–molecular weight heparin (LMWH) is used clinically to treat clotting disorders. As an animal-sourced product, LMWH is a highly heterogeneous mixture, and its anticoagulant activity is not fully reversible by protamine. Furthermore, the reliability of the LMWH supply chain is a concern for regulatory agencies. We demonstrate the synthesis of heparin dodecasaccharides (12-mers) at the gram scale. In vitro experiments demonstrate that the anticoagulant activity of the 12-mers could be reversed using protamine. One of these, labeled as 12-mer-1, reduced the size of blood clots in the mouse model of deep vein thrombosis and attenuated circulating procoagulant markers in the mouse model of sickle cell disease. An ex vivo experiment demonstrates that the anticoagulant activity of 12-mer-1 could be reversed by protamine. 12-mer-1 was also examined in a nonhuman primate model to determine its pharmacodynamic parameters. A 7-day toxicity study in a rat model showed no toxic effects. The data suggest that a synthetic homogeneous oligosaccharide can replace animal-sourced LMWHs.

Heparin was isolated from an unusually large human hemangioma that contained an elevated level of mast cells. Purification of multimilligram quantities of heparin from this tissue sample permitted a thorough examination of its structure and activity. Characterization of this human heparin included the following: one-dimensional and two-dimensional 1H-nuclear magnetic resonance spectral analysis; oligosaccharide mapping; saccharide compositional analysis; and in vitro assessment and anticoagulant activity. Oligosaccharide mapping and nuclear magnetic resonance spectroscopy showed that this human heparin is structurally similar to porcine intestinal mucosal heparin but distinctly different from bovine lung heparin. This human heparin also has substantially more in vitro anticoagulant activity than either of these pharmaceutical heparins.

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Heparin and its low-molecular-weight heparin (LMWH) derivatives are widely used clinical anticoagulants. These drugs are critical for the practice of medicine in applications including kidney dialysis, cardiopulmonary bypass, and in the management of venous thromboembolism. Currently, these drugs are derived from livestock, primarily porcine intestine. The worldwide dependence on a single animal species has made the supply chain for this critical drug quite fragile, leading to the search for other sources of these drugs, including bovine tissues such as bovine intestine or lung. A number of laboratories are currently examining the similarities and differences between heparins prepared from porcine and bovine tissues. The current study is designed to compare LMWH prepared from bovine heparins through chemical β-elimination, a process currently used to prepare the LMWH, enoxaparin, from porcine heparin. Using top-down, bottom-up, compositional analysis and bioassays, LMWHs, derived from bovine lung and intestine, are shown to closely resemble enoxaparin.

Andexanet alfa is a recombinant factor Xa decoy protein, designed to reverse bleeding associated with oral anti-Xa agents. Andexanet alfa is also reported to neutralize the effects of heparin-related drugs. This study focused on the neutralization profiles of unfractionated heparin (UFH), enoxaparin, and, a chemically synthetic pentasaccharide, fondaparinux by andexanet alfa. Whole blood clotting studies were carried out using thromboelastography (TEG) and activated clotting time (ACT). The anticoagulant profile of UFH, enoxaparin, and fondaparinux was studied using the activated partial thromboplastin time (aPTT), thrombin time (TT), and amidolytic anti-Xa, and anti-IIa methods. Thrombin generation inhibition was studied using the calibrated automated thrombogram system. Reversal of each of these agents was studied by supplementing andexanet alfa at 100 µg/mL. In the TEG, andexanet alfa produced almost a complete reversal of the anticoagulant effects of UFH and enoxaparin; however, it augmented the effects of fondaparinux. In the ACT, aPTT, and TT, UFH produced strong anticoagulant effects that were almost completely neutralized by andexanet alfa. Enoxaparin produced milder anticoagulant responses that were partially neutralized, whereas fondaparinux did not produce any sizeable effects. In the anti-Xa and anti-IIa assays, UFH exhibited partial neutralization whereas enoxaparin and fondaparinux did not show any neutralization. All agents produced varying degrees of the inhibition of thrombin generation, which were differentially neutralized by andexanet alfa. These results indicate that andexanet alfa is capable of differentially neutralizing anticoagulant and antiprotease effects of UFH and enoxaparin in an assay-dependent manner. However, andexanet alfa is incapable of neutralizing the anti-Xa effects of fondaparinux.