Activated protein C accelerates venous thrombus resolution through heme oxygenase-1 induction.

Summary Background Thrombus resolution is a complex process that involves thrombosis, leukocyte-mediated thrombolysis, and the final resolution of inflammation. Activated protein C (APC) is an anticoagulant that also possesses immunoregulatory activities. Aim In this study, we sought to examine the effects of APC administration on thrombus resolution using a mouse model of deep vein thrombosis by ligating the inferior vena cava (IVC). Methods The IVCs of C57BL/6 mice were ligated. Beginning on day 4 post IVC ligation, mice were injected intraperitoneally daily with APC, APC plus an heme oxygenase-1 (HO-1) inhibitor Sn-protoporphyrin IX (SnPP), SnPP alone, or vehicle control. At different time points following surgery, the thrombus-containing IVCs were weighed and then analyzed by use of biochemical assays and histology. Results Venous thrombi reached maximum size on day 4 post ligation. The APC-treated group exhibited a significant reduction in thrombus weights on day 12 but not on day 7 compared with control mice. The enhanced thrombus resolution in APC-treated mice correlated with an increased HO-1 expression and a reduced interleukin-6 production. No significant difference was found in urokinase-type plasminogen activator, plasminogen activator inhibitor-1, or matrix metalloproteinase-2 and -9 between APC-treated and control mice. Coinjection of the HO-1 inhibitor SnPP abolished the ability of APC to enhance thrombus resolution. Conclusions Our data show that APC enhances the resolution of existing venous thrombi via a mechanism that is in part dependent on HO-1, suggesting that APC could be used as a potential treatment for patients with deep vein thrombosis to accelerate thrombus resolution.