TISSUE FACTOR PATHWAY INHIBITOR IN COMPLEX WITH LOW-DENSITY-LIPOPROTEIN ISOLATED FROM HUMAN PLASMA DOES NOT POSSESS ANTICOAGULANT FUNCTION IN TISSUE FACTOR-INDUCED COAGULATION IN-VITRO

Tissue factor pathway inhibitor (TFPI) is a potent inhibitor of the ex trinsic coagulation system. In human plasma 70-85% is associated with apoB-containing lipoproteins whereas 10-20% exists in a carrier free f orm. The purpose of the present study was to assess the anticoagulant function of TFPI in complex with low density lipoproteins (LDL) on tis sue factor (TF)-induced coagulation in vitro. LDL-TFPI complexes were isolated by preparative density gradient ultracentrifugation, LDL-free TFPI by preparative gel filtration and the anticoagulant properties w ere assessed by a diluted prothrombin time assay(dPT). LDL-free TFPI ( 0-0.46 U/ml) added to the dPT mixture, caused a prominent dose-depende nt prolongation of dPT (0-42.2 sec.) which could be abolished by the a ddition of blocking anti-TFPI IgG. Contrary, increasing amounts of LDL -bound TFPI (0-4.0 U/ml) shortened dPT by 11.4 sec at the highest conc entration. LDL-bound TFPI was not immunodetected by anti-TFPI IgG dire cted against the distal portion of the C-terminus, and appeared on Wes tern blotting with a major band at 67 kDa and a weak band at 34 kDa wh ich suggest that LDL-bound TFPI lack anticoagulant function due to car boxy terminal truncation. Our data provide evidence for the hypothesis that the anticoagulant function of TFPI is restricted to its carrier free form in human plasma. (C) 1997 Elsevier Science Ltd.