Cellular and Enzymatic Features of Thrombi in Humans Are Vascular Bed-Dependent

• Thrombus age determines inflammatory and fibrotic capabilities through activation of enzymes that are known to damage the blood vessel wall.

• Subacute or chronic thrombus in veins contains higher MMP9 activity than acute thrombus extracted from arteries. MMP9 appears to come from macrophages in thrombus.

Mechanisms behind vascular remodeling following thrombosis are unclear. While acute arterial thrombosis in the cerebrovascular circulation has devastating consequences and requires immediate attention, management of venous thromboembolism (VTE) varies significantly. Our goal was to determine molecular signatures and cellular content of thrombus extracted by catheter to gain insight into vascular remodeling. Twenty-five patients underwent catheter-directed thrombectomy (CDT); 13 for cerebrovascular accident (CVA), 8 for pulmonary embolism (PE), and 4 for deep vein thrombosis (DVT). Protein and RNA were extracted from thrombi to enable immunoblotting, RNA sequencing, and quantification of gene expression. Time from symptom onset to thrombus extraction was 7.7 ± 1.9 hours for CVA and 109 ± 55 hours VTE. Protein concentration, white blood cell content (monocytes), and red blood cell content were greater in venous compared with arterial thrombus while platelet content was similar. Both venous and arterial thrombi contained several zinc endopeptidases belonging to the Matrix Metalloproteinase (MMP) family. MMP9 activity in venous thrombus was greater than arterial thrombus (61 ± 9 ng/mL.μg protein^-1 vs. 25 ± 6 ng/mLμg protein^-1, P=0.005). Arterial and venous thrombus display surprisingly different phenotypes, with biologically-active enzymes promoting blood vessel remodeling, and enzymatic activity proportional to thrombus age extracted from veins. These mechanistic data may support a role for early CDT in the venous circulation to avoid irreversible vascular remodeling.