Structural analysis of endothelial cell mediated prolongation of t-PA driven lysis of an “aged clot”
In an effort to reestablish blood flow in blocked coronary arteries, heart attack victims are now routinely treated with thrombolytic (clot busting) drugs. However, thrombolytic therapy fails to restore sufficient flow in approximately 20% of cases. The reasons for these failures are undoubtedly multifactorial and difficult to study in vivo. We have developed an “in vitro” model blood vessel which allows controlled study of factors influencing thrombolysis. In the studies reported here, we investigated the 3-D distribution of HUVEC secreted PAI-1 within the clot using immuno-gold cytochemistry and intermediate voltage electron microscopy (IVEM).Human umbilical vein endothelial cells (HUVEC) were grown on the inside surface of fibronectin-coated glass tubes. The cells are stimulated for 4 hours with 1000 U/ml of TNF-α. Clot formation was initiated by addition of 2.3 μM fibrinogen, 100 nM plasminogen, and then 2 nM thrombin in HEPES buffered Gey's salts + 0.5% human serum albumin. After aging the clot for up to 4 hours (to mimic the time delay between heart attack and treatment), 0.5 nM rt-PA (thrombolytic agent) was perfused through the clot for 10 min. at 5 ml/hr. Formation and dissolution of the clot were monitored by laser light scattering.