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Unfractionated heparin promotes elimination of human recombinant mammalian TFPI in a rat model

Abstract number: PP-MO-177

Øie¹ C., Brodin¹ E., Hilden² I., Appa² R., Smedsr⊘d³ B., Hansen¹ J.B.

¹¹Center for Atherothrombotic Research, Department of Medicine, Troms, Norway ²²Biopharmaceuticals Research Unit, Novo Nordisk, Mål⊘v, Denmark ³³Institute of Medical Biology, Department of Cell Biology and Histology, Troms, Norway

How-to-cite Øie C, Brodin E, Hilden I, Appa R, Smedsr⊘d B, Hansen JB. Unfractionated heparin promotes elimination of human recombinant mammalian TFPI in a rat model. Journal of Thrombosis and Haemostasis 2009; Volume 7, Supplement 2: Abstract PP-MO-177

TFPI is a potent inhibitor of TF-factor VIIa complex and a direct inhibitor of factor Xa mainly synthesized by and associated with endothelial cells in the circulation. TFPI plays an important role for the anticoagulant effect of heparin, but prolonged administration of UFH is known to cause partial depletion of intravascular TFPI, despite the fact that UFH upregulates the synthesis and release of TFPI in ECs. Thus, the depletion of intravascular TFPI by UFH, and not by LMWH has been suggested to explain the superiority of LMWH in both arterial and venous thrombosis. The aim of the study was to elucidate the effect of heparin treatment on the cellular basis of clearance of recombinant full length mammalian TFPI (m-TFPI) compared to bacterial TFPI (b-TFPI) in a rat model.

Methods: Male Sprague–Dawley rats were used as research animals. Recombinant full-length TFPI expressed in bacteria (E. coli) and mammalian cells (BHK) was labelled with 125I, and used to study clearance in vivo and in vitro on primary parenchymal cell (PC)and liver sinusoidal endothelial cells(LSEC) cultures isolated from rat liver.

Results: Both types of TFPI formed complexes with UFH in vitro, assessed by SPR analysis.I.v administration of 100 IU/kg UFH immediately prior to TFPI decreased the circulatory survival of m-TFPI from 1.86 ± 0.20 min to 0.43 ± 0.08 min (P < 0.001) without affecting the clearance of b-TFPI. Hepatocellular distribution of radiolabeled ligands showed that both forms of TFPI were mainly taken up by PCs in the absence of UFH. UFH administration switched the hepatocellular distribution of b-TFPI from PCs towards LSECs, without affecting the distribution of m-TFPI. Presence of UFH did not affect cellular binding, but increased degradation of m-TFPI in primary cultures of PCs.

Conclusions: Our findings suggest that depletion of intravascular TFPI during prolonged UFH treatment is caused by shortened circulatory survival of TFPI during heparin treatment. Formation of heparin-TFPI complexes during heparin treatment directed b-TFPI towards LSEC, the principal site for UFH elimination, without affecting m-TFPI uptake in PCs. These observations may suggest that the PC receptor(s)for m-TFPI had higher affinity for its ligand than the receptor for b-TFPI(LRP) in the presence of UFH.

Disclosure of interest: none declared.

To cite this abstract use the following format:

Journal of Thrombosis and Haemostasis 2007; Volume 5, Supplement 2: abstract number

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