The effect of recombinant tissue factor pathway inhibitor (rTFPI) on e
xtracellular matrix procoagulant activity was studied in a human ex vi
vo model of thrombogenesis. Extracellular matrix of endotoxin stimulat
ed endothelial cells perfused with human non-anticoagulated blood at a
wall shear rate of 100/s induced pronounced fibrin deposition, which
covered 82 +/- 11% of the matrix surface within 5 min. Preincubating t
he matrix with the combination of rTFPI, factor VIIa (FVIIa) and facto
r Xa (FXa) reduced fibrin deposition to levels observed with matrix fr
om non-stimulated endothelial cells (7 +/- 6% fibrin coverage, P < 0.0
01). Preincubation with rTFPI plus FXa also reduced fibrin deposition
significantly, but to a lesser extent (41 +/- 6% fibrin coverage, P <
0.001). Preincubation with rTFPI alone, or with rTFPI plus FVIIa, did
not affect fibrin deposition. The inhibition of thrombus formation on
procoagulant extracellular matrix by rTFPI seemed to be FXa-dependent,
and a result of TFPI's ability to bind and inhibit both TF activity a
s well as FXa. The results from this study suggest a future role for r
TFPI as an agent for prevention of TF-induced vascular thrombosis.