Inhibitors of phosphodiesterase (pentoxifylline, trequinsin) inhibit apical and subcellular matrix expression of tissue factor in cultured human endothelial cells.

Exposure of endothelial cells (ECs) to thrombin or cytokines leads to major changes in their biochemical properties, which confer procoagulant activities. Stimulated ECs express the procoagulant glycoprotein tissue factor (TF). Although some TF is expressed on the apical surface of the cells, most is deposited as a cryptic pool in the subendothelial matrix. This matrix-associated TF may play a role in thromboembolic complications associated with alterations in the integrity of the EC monolayer. We have measured TF activity on the surface and in the subcellular matrix of human saphenous vein ECs in culture, by assaying the TF-dependent formation of activated factor X in the presence of factor VII. The subcellular matrix was prepared by exposure of ECs to ammonium hydroxide. Incubation of ECs for 4 h with 1 U/ml human thrombin induced TF expression on the apical cell surface and in the matrix. Activity in the matrix was 4.1 +/- 0.5 times greater than on the cell surface. Pentoxifylline inhibited the expression of TF both on the cell surface and in the matrix. The EC50 was on the order of 3.9 mM in both cases. No signs of cell toxicity were observed at this concentration of pentoxifylline. Similar effects were obtained with trequinsin (HL 725), a phosphodiesterase inhibitor, with an EC50 of 40 microM. This suggests that an increase in cAMP may be involved in the mechanism of action of pentoxifylline. Inhibition of TF deposition in the matrix may be important in the prevention of thromboembolic episodes in conditions where ECs either retract or are removed by major injury.