Summary
Heparin and low molecular weight heparins (LMWHs) have both antithrombotic and anti-angiogenic
activities. The antiangiogenic activity of LMWH may be associated with the release
of endothelial tissue factor pathway inhibitor (TFPI), an important endogenous inhibitor
of tissue factor/Factor VIIa (TF/fVIIa).To evaluate the effects of LMWH, tinzaparin,
and TFPI in a model of angiogenesis-mediated processes, we compared the effects of
tinzaparin, and recombinant TFPI in inhibiting either basic fibroblast growth factor-2
(FGF2) or TF/fVIIainduced endothelial cell tube formation in human umbilical vein
endothelial cells (HUVEC).Our results show that tinzaparin and recombinant TFPI both
blocked endothelial tube formation induced by either FGF2 or TF/fVIIa, in a concentration-dependent
manner. Endothelial tube formation was only marginally inhibited by a potent and specific
anti-Factor Xa, recombinant tick anticoagulant protein (rTAP). A monoclonal anti-TFPI
antibody reversed the inhibitory effects of either tinzaparin or recombinant-TFPI
on HUVEC tube formation. Tinzaparin fractions in the range of 8,000 to 12,600 Da were
most effective in stimulating the release of TFPI from HUVEC. These results suggest
that the inhibitory effect of the LMWH tinzaparin on endothelial tube formation is
associated with stimulation of the release of TFPI, but not to anti-Factor Xa activity.
Keywords
Low molecular weight heparin - tinzaparin - endothelial cell tube formation - tissue
factor pathway inhibitor