Inhibition of Heparinase I by Defibrotide: Potential Clinical Implications

Abstract

Defibrotide is an anti-ischemic/antithrombotic agent used to treat transplantation associated vascular complications. Defibrotide releases endogenous antithrombotic mediators. Co-administration of defibrotide with heparin augments the effect of heparin and increases its biologic half-life. The effects of defibrotide and its fractions on heparinase I mediated digestion of heparin were investigated. A fixed concentration of heparin was subjected to Flavobacterium heparinicum heparinase I in the presence of graded amounts of defibrotide/fractions (6.25 to 250 μg/ml). The extent of heparin digestion was determined using HPLC and computation of the oligosaccharide profiles. Heparinase I digested heparin (MW = 15.2 kDa) to a low molecular mass heparin (MW = 4.1 kDa). At concentrations >125 μg/ml, defibrotide produced an almost complete inhibition of digestion. The IC50 value for this reaction was 12.5 μg/ml. A molecular weight dependence on the inhibition of heparinase was noted. Studies in primates revealed that the anticoagulant effects of both unfractionated and low molecular mass heparins are potentiated by defibrotide as determined by AUC measurements of the circulating level of these agents. The potentiation of the anticoagulant effect of heparin in patients treated simultaneously with defibrotide may be due in part to the inhibition of endogenous heparin degrading enzymes. These interactions should be taken into account to optimize anticoagulant management where these drugs are used in a combination regimen.