Tissue Factor Pathway Inhibitor Activity in Human Plasma: Measurement of Lipoprotein-Associated and Free Forms in Hyperlipidemia

Tissue factor pathway inhibitor (TFPI), a protease inhibitor that is present in free and lipoprotein-associated forms in plasma and that also occurs as an endothelial cell-associated form, can inhibit the initial reactions of the tissue factor-mediated coagulation pathway. Although a positive correlation between plasma TFPI activity and cholesterol concentration in human plasma has been demonstrated, levels of the various forms of TFPI, ie, the LDL/VLDL-associated form, the HDL-associated form, and the free form, have not yet been completely determined in hyperlipidemia. We therefore established a method for the measurement of each of these forms of TFPI in plasma by gel filtration of plasma in buffer containing 1 mol/L NaCl. The recovery of TFPI activity in the free form was markedly greater as assessed by the new method than the recovery reported when other methods have been used. We employed the new method to analyze TFPI activity in 19 hyperlipidemic patients and compared the results with those for normal control subjects. The level of LDL/VLDL-associated TFPI in hyperlipidemic patients was significantly increased compared with control subjects' levels (0.383 plus/minus 0.112 versus 0.237 plus/minus 0.077 U/mL), whereas the level of the free form of TFPI in hyperlipidemic patients was significantly decreased (0.381 plus/minus 0.132 versus 0.495 plus/minus 0.106 U/mL), the former being positively correlated with cholesterol level, while the latter was negatively correlated. These results led us to speculate that the decrease in the free form of TFPI in hyperlipidemia was caused by an increase in LDL/VLDL and/or by the inhibition of TFPI synthesis in endothelial cells; such an inhibition may reflect a reduction in the antithrombotic function of vascular endothelial cells. Of note, the decrease in the free form of TFPI was more striking in patients receiving plasmapheresis treatment (0.271 plus/minus 0.089 U/mL); this decrease was due to the repeated removal of LDL/VLDL-associated TFPI and endothelial cell-associated TFPI. (Arterioscler Thromb Vasc Biol. 1995;15:504-510.).