Background: Thrombosis is a common complication in cancer patients receiving chemotherapy regimens that include cyclophosphamide. However, the mechanisms by which these agents increase this risk are largely uncharacterized.
Objectives: To examine the effects of cyclophosphamide and its metabolite acrolein on procoagulant and anticoagulant pathways in both cell-based and animal-based models.
Methods: Thrombin and activated protein C (APC) generation were measured in defibrinated plasma exposed to acrolein-treated endothelial and smooth muscle cells. Tissue factor (TF) activity was measured on acrolein-treated cells. Cell surface levels of phosphatidylserine, TF, endothelial protein C receptor and thrombomodulin were measured. Healthy BALB/c mice received injections of saline (control), acrolein, or cyclophosphamide; blood was collected, and plasma thrombin-antithrombin (TAT) complex, protein C and APC levels were analyzed.
Results: Exposure of acrolein-treated endothelial and smooth muscle cells to defibrinated plasma increased thrombin generation in the plasma. This was associated with enhanced phosphatidylserine exposure and/or increased TF activity on acrolein-treated cells. Despite elevated levels of thrombin generation, plasma APC levels were not elevated. In vivo, treatment of mice with cyclophosphamide and acrolein resulted in elevations of plasma TAT complex levels, whereas APC levels remained low.
Conclusions: This is the first study to examine thrombin generation and the APC pathway in chemotherapy-treated mice. Cyclophosphamide and acrolein appear to upregulate procoagulant pathways, while impairing endogenous anticoagulant pathways. This may explain, in part, the increased risk of thrombosis observed in cancer patients receiving cyclophosphamide-containing chemotherapy.
© 2011 International Society on Thrombosis and Haemostasis.