Pharmacokinetics and delayed experimental antithrombotic effect of two domain nonglycosylated Tissue Factor Pathway Inhibitor.

Tissue Factor Pathway Inhibitor(TFPI) is a naturally occurring inhibitor of the TF-FVIIa induced coagulation in the presence of FXa. Recombinant two domain TFPI, where Asn 117 on the FXa-inhibitory domain was exchanged to a Gin yielding non-glycosylated TFPI (117QTFPl(1-161)), was evaluated regarding pharmacokinetics and delayed antithrombotic potential in the rabbit. Pharmacokinetic study; 117QTFPI(1-161) vs glycosylated TFPI1-161. Three rabbits/group were used and received 1,0 mg/kg a bolus iv injection. Plasma-TFPI was measured for three hours. The alpha-phase half-life was similar, the beta-phase half-life was close to four times longer for 117QTFPI(1-161) (37 vs 10 min). Clearance of 117QTFPI(1-161) was nearly two times lower (45 vs 21 ml/kg/min). Delayed anti-thrombotic study; 10 rabbits/group were used. 5 Groups; placebo+placebo, placebo+LMWH 60 anti-Xa IU/kg, placebo+117QTFPI(1-161) 0,25 mg/kg, 117QTFPI(1-161) 1,0 and 4,0 mg/kg+placebo. First injection 60 min prior to the second one, which coincided with the thrombus induction. The experimental thrombosis used combines a chemical destruction of the endothelium with a partial restriction of the bloodflow in the jugular veins. The thrombusweight was significantly reduced in LMWH and 117QTFPI(1-161) 1,0 and 4,0 mg/kg groups (0,6-2,6 vs 11,8 mg). Frequency of occlusive thrombosis was significantly reduced in the LMWH and 117QTFPI(1-161) 4,0 mg groups. All groups significantly effected the aXa-assay, the LMWH-group the most (0,85 IU/ml). LMWH was the only substance to prolong the dilute-PT-assay at the different timepoints. Absence of glycosylation increases the beta-phase half-life and decreases clearance of two domain TFPI. 117QTFPI(1-161)(1,0 and 4,0 mg) has an antithrombotic effect indistinguishable from LMWH even though given 60 min before the thrombusinduction but with a considerable less effect on anti-Xa, APTT and no effect on dilute-PT. Glycosylation of TFPI influences the pharmacokinetics but not the antithrombotic capacity in this experimental setting.