Introduction: There is an increase in the natural level of urokinase-type plasminogen activator (uPA) activity within the thrombus during venous thrombus resolution. The use of uPA as a thrombolytic agent in the treatment of acute iliofemoral deep vein thrombosis is not suitable for all patients. This study aimed to determine whether thrombus resolution could be enhanced by upregulating uPA expression using adenoviral gene transfer as an alternative method of delivery.
Methods: The production of functional uPA by an adenoviral gene construct (ad.uPA) was confirmed by a colorimetric substrate assay and fibrin plate lysis. Thrombus was formed in the inferior vena cava of wild-type mice and injected, 48-hours after induction, with either a control virus at 10(8) plaque-forming units (pfu) or ad.uPA at 10(7) or 10(8) pfu. Thrombi were removed and weighed 7 days after treatment. Activity of metalloproteinase (MMP) 2 and 9 was measured by zymography and the release of vascular endothelial growth factor (VEGF) and D-dimer levels by enzyme-linked immunoabsorbent assay. The results were expressed as a mean +/- SEM. Values were standardized for wet weight or for soluble protein content (mg/sol protein).
Results: Treatment with ad.uPA reduced thrombus weight by twofold compared with thrombi treated by control virus (15.1 +/- 1.1 mg vs 7.4 +/- 1.3 mg, P = .004). Urokinase activity (17 +/- 3 pg/mg wet weight) was detected in all treated thrombi, but there was no dose-dependent effect. D-dimer activity was increased twofold after treatment with ad.uPA (1.7 +/- 0.15 ng/mg of sol protein vs 0.8 +/- 0.1 ng/mg of sol protein, P = .0015) and was associated with a reduction in thrombus size (P = .03). Urokinase overexpression did not affect the activity of MMP2, MMP9, or VEGF in the thrombus.
Conclusion: Increasing urokinase activity within the thrombus significantly enhanced natural thrombus resolution by a fibrinolytic action. Therapeutic delivery of ad.uPA in patients may provide a novel method of treating deep vein thrombosis.
Clinical relevance: The use of urokinase as a thrombolytic agent in the treatment of acute iliofemoral deep vein thrombosis is not suitable for all patients. This study aimed to determine whether thrombus resolution could be enhanced by upregulating urokinase expression using adenoviral gene transfer as an alternative method of therapeutic delivery. The study shows that by increasing urokinase activity within the thrombus, natural thrombus resolution can be significantly enhanced. The delivery of ad.uPA in patients may provide a novel method of treating deep vein thrombosis.