Venous but Not Arterial Thrombus is Biologically Active: Cellular and Enzymatic Contributions

Background: Acute arterial thrombosis has devastating consequences, but urgency is rarely a factor in treating venous thrombosis, especially in the legs. Our goal was to determine the cellular content and enzymatic activity of catheter-extracted thrombus to gain insight into vascular remodeling. Methods: Catheter-extracted thrombosis in 27 patients with VTE (deep vein thrombosis [DVT, n=5], pulmonary embolism [PE, n=9]) and thrombotic stroke (AT, n=13) was evaluated by 2-dimensional electrophoresis, and immunoblotting (IB) for markers of platelets: (CD41), white blood cells (WBC, CD45), and red blood cells (RBC, CD235A ). Matrix metalloproteinase (MMP) isoforms were determined by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) and confirmed by IB. Total MMP activity was determined by zymography, then isoform catalytic activity was validated using chromogenic substrates. Results: Protein concentration in 7mg thrombus was greater in VTE vs. AT (p=0,046). CD41 was similar in VTE vs. AT thrombus while CD45 (p=0.047) and CD235A (P=0.001) were greater in VTE. Only CD235A was greater in PE vs. DVT thrombus (P=0.002). Zymography identified enzymatic activity of many MMP isoforms. Of the 10 MMP isoforms assessed, only the following were identified in both VTE and AT: MMP 1,2,8,9,10,14. Protein content was greater in VTE vs. AT by IB for: MMP1 0.79±0.13 vs. 0.43±0.12, p=0.02, MMP2 (0.30±0.08 vs. 0.17±0.03, p=0.05), and MMP9 (1.3±0.38 vs. 0.26±0.06, p=0.009). MMP9 activity was far greater in thrombus from patients with VTE vs. AT (25 U±5.6 vs. 63±8.1 ng/mL.(μg protein) -1 protein, p=0.0008). Conclusion: Cellular composition of thrombus in different vascular beds varies, altering susceptibility to tissue plasminogen activator and the potential for thrombus to irreversibly remodel blood vessels. Thrombus-derived biomarkers driving decisions for catheter-extraction should be prospectively evaluated in patients with VTE.