MEASUREMENT OF THE FREE-FORM OF TFPI ANTIGEN IN HYPERLIPIDEMIA - RELATIONSHIP BETWEEN FREE AND ENDOTHELIAL CELL-ASSOCIATED FORMS OF TFPI

Tissue factor pathway inhibitor (TFPI), a protease with three tandem K unitz-type (K1, K2 and K3) domains, inhibits the initial reaction of t he: TF-mediated coagulation pathway. TFPI occurs in a free and a lipop rotein-associated form in plasma as well as an endothelial cell-associ ated form on vascular walls. In a previous study we had demonstrated t hat free-form TFPI activity was lower in hyperlipidemic patients. In t he present study we established a new enzyme immunoassay method for me asuring free-form TFPI antigen; this new method uses a monoclonal anti body that recognizes the K3 domain for free-form TFPI but not lipoprot ein-associated TFPI. Free-form TFPI antigen was significantly lower in hyperlipidemic patients compared with those in normolipidemic individ uals, We applied this new method to measure the amount of endothelial cell-associated TFPI, which can be released by heparin injection, as ' 'free-form TFPI.'' We found that free-form TFPI antigen in plasma was positively correlated with the endothelial cell-associated form. These results indicate that both of these forms of TFPI are in equilibrium in vivo and that our new method can lie used for assessing changes in the levels of endothelial cell-associated TFPI antigen and, hence, for assessing thrombotic tendencies in various disease stares.