Submitted June 13, 2008
Accepted August 6, 2008
Low plasma levels of tissue factor pathway inhibitor
in patients with congenital factor V deficiency
Connie Duckers, Paolo Simioni, Luca Spiezia, Claudia Radu, Sabrina Gavasso, Jan Rosing, and Elisabetta Castoldi*
Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, Maastricht, Netherlands
Department of Medical and Surgical Sciences, University of Padua Medical School, Padua, Italy
* Corresponding author; email: e.castoldi{at}bioch.unimaas.nl.
Severe factor V (FV) deficiency is associated with a mild-to-severe bleeding diathesis, but many patients with FV levels <1% bleed less than anticipated. We used Calibrated Automated Thrombography to screen patients with severe FV deficiency for protective procoagulant defects. Thrombin generation in FV-deficient plasma was only measurable at high tissue factor concentrations. Upon reconstitution of FV-deficient plasma with purified FV, thrombin generation increased steeply with FV concentration and reached a plateau at ~10% FV. FV-deficient plasma reconstituted with 100% FV generated several-fold more thrombin than normal plasma, especially at low tissue factor concentrations (1.36 pM) or in the presence of activated protein C, suggesting reduced tissue factor pathway inhibitor (TFPI) levels in FV-deficient plasma. Plasma TFPI antigen and activity levels were indeed lower (p<0.001) in FV-deficient patients (n=11, 4.0±1.0 ng/ml free TFPI) than in controls (n=20, 11.5±4.8 ng/ml), while individuals with partial FV deficiency had intermediate levels (n=16, 7.9±2.5 ng/ml). FV-immunodepletion experiments in normal plasma and surface plasmon resonance analysis provided evidence for the existence of a FV/TFPI complex, possibly affecting TFPI stability/clearance in vivo. Low TFPI levels decreased the FV requirement for minimal thrombin generation in FV-deficient plasma to <1% and might therefore protect FV-deficient patients from severe bleeding.
