Does glycosylation influence the experimental antithrombotic effect of a two-domain tissue factor pathway inhibitor?

We have earlier shown that both full-length and truncated glycosylated tissue factor pathway inhibitor (TFPI) lacking the third Kunitz domain and the c-terminal region has an antithrombotic effect comparable to lowmolecular-weight heparin (LMWH) in an experimental venous thrombosis model. The aim of this study was to investigate whether a recombinant truncated non-glycosylated TFPI (117QTFPI1-161) had an antithrombotic effect similar to the glycosylated TFPI1-161 and LMWH. We also followed the coagulation parameters. The thrombi were induced in rabbit jugular veins with a combination of endothelium destruction and restricted blood flow. Group 1: placebo; group 2: LMWH 60 anti-Xa IU/kg, i.v.; groups 3 and 4: TFPI1-161 0.8 and 0.2 mg/kg, i.v., respectively; groups 5 and 6: 0.8 and 0.2 mg/kg 117QTFPI1-161, i.v., respectively, in a randomized double-dummy fashion. Twelve animals were included in the placebo group and 6 in each of the other groups. The frequency of thrombosis and also of occlusive thrombosis was reduced in all groups compared to placebo. The thrombus weight was reduced (0-9.9 mg) in all groups, significantly in groups 2, 4 and 5 (p = 0.004-0.02) compared to placebo (21.1 mg). In group 3, a borderline p value was achieved (0.06 likely a beta-error). The two forms of TFPI1-161 given in the higher doses showed a significantly greater increase of anti-Xa activity, but with a shorter duration compared to LMWH (1.7-1.9 vs. 0.9 anti-Xa IU/ml). Activated partial thromboplastin time (aPTT)-analysis revealed that only LMWH (52 s) caused a significant transient elevation 2 min after injection. In the other groups, a temporary but insignificant elevation of aPTT (27-37 s) was seen. No detectable effect on anti-IIa activity and prothrombin time (PT) was seen in any TFPI group. The glycosylation of the second domain on TFPI does not substantially contribute to the antithrombotic effect of TFPI. Regardless of the glycosylation of TFPI1-161, it has a dose-dependent effect on anti-Xa, a small effect on the aPTT, but no effect on anti-Ila and PT. LMWH has a more pronounced and sustained impact on these parameters.