Abstract 75: Heparanase Mediates Arteriothrombosis Following Vascular Injury or Endovascular Stenting

Abstract

Background: Heparanase cleaves heparan sulfate proteoglycans (HSPGs), key components of the extracellular matrix and critical endothelial mediators of hemostasis. Our previous work has shown that heparanase levels are elevated in atherosclerosis and following endovascular stenting. Methods: We used mice overexpressing human heparanase and examined the time to thrombosis using a laser induced arterial thrombosis model in combination with vascular injury. An ex-vivo system was used to examine the formation of thrombus to stent-induced flow disturbance. To evaluate thrombotic potential in wild-type (WT) or heparanase transgenic (HPA-Tg) mice, the left common carotid artery was isolated and a vascular flow probe was used to monitor blood flow. Rose Bengal dye was injected into the mice and the mid portion of the common carotid artery was then illuminated with a 1.5-mW green laser (540 nm) until an occlusive thrombus was formed. Arterial injury was also performed prior to measuring thrombosis to examine the effects of light and heavy injury on thrombosis in WT and HPA-Tg mice. A novel ex-vivo assay of stent thrombosis was performed in which mouse aortas were stented into a modified Chandler loop and the loops were perfused with blood from transgenic mice. Results were analyzed with electron microscopy and optical absorbance for clot formation. Results: In the absence of injury there was no difference in the time for formation of thrombus in the WT and HPA-Tg mice. However in the presence of arterial injury, thrombosis in HPA-Tg mice occurred significantly faster than in WT mice (light injury: 67.7 minutes vs. 39.8 minutes, p<0.05; heavy injury: 63.0 minutes vs. 41.8 minutes, p<0.05). The prothrombotic phenotype of heparanase transgenic mice is masked when heparin is administered prior to injury (WT: 68.5 minutes vs. HPA Tg: 69.2 minutes p=NS). Blood from heparanase transgenic mice also increased stent thrombosis threefold in flow loops as measured by optical density (2.8 vs. 1.0 optical density, p<0.05) and increased adherent platelets were found in electron microscopy. Conclusions: Increased arterial expression of heparanase leads to enhanced risk of thrombosis in the injured artery. In particular, endovascular stenting induces both injury and flow disturbance that exacerbate the thrombotic potential of blood with increased heparanase levels.