F. Kassam1, M. C. Morris1, A. Bercz1, R. Veile1, L. Friend1, N. Beckmann1, C. C. Caldwell1, M. D. Goodman1 1University Of Cincinnati,Department Of Surgery, College Of Medicine,Cincinnati, OH, USA
Introduction: The pathophysiology behind the subacute but persistent hypercoagulable state following traumatic brain injury is poorly understood but contributes to morbidity induced by venous thromboembolism (VTE). Because platelets and their microvesicles have been hypothesized to play a role in posttraumatic hypercoagulability, administration of commonly utilized agents for inflammation, VTE chemoprophylaxis, and sphingolipid modulation may ameliorate this coagulability. We hypothesized that utilization of aspirin, ketorolac, amitriptyline, unfractionated heparin, and enoxaparin would modulate the platelet and whole blood coagulation response following traumatic brain injury.
Methods: A standard weight-drop system was utilized to induce concussive traumatic brain injury in mice. Following injury, mice were randomized into drug treatment groups to receive aspirin (100 mg/kg), ketorolac (5 mg/kg), amitriptyline (10 mg/kg), heparin (75 IU/kg), enoxaparin (3 mg/kg), or saline control (100µL) at 2 and 8 hours post-TBI. Mice were then sacrificed at 6 or 24 hours after injury and blood was drawn via cardiac puncture to determine coagulability by thromboelastometry (EXTEM and FIBTEM), platelet function testing with impedance aggregometry, and microvesiscle enumeration utilizing nanoparticle tracking analysis.
Results: Thromboelastometry results demonstrated that the platelet contribution to maximum clot firmness (%MCF-Platelet) at 6 hours (Figure 1) was significantly higher in mice that received aspirin (69%, p<0.002) or amitriptyline (68%, p<0.007) compared to mice that received saline (57%). At 24 hours, the %MCF-Platelet remained significantly higher in mice that received amitriptyline (66%, p=0.04) compared to those that received saline (63%). The overall ADP- and arachidonic acid-induced platelet aggregation was significantly lower in mice receiving ketorolac, aspirin, and amitriptyline compared to mice receiving saline at 6 hours post-injury. By 24 hours after injury, mice that received aspirin (40 a.u., p<0.005), ketorolac (38 a.u., p=0.02), and enoxaparin (35 a.u., p=0.04) had significantly lower ADP-induced platelet aggregation than saline control mice (54 a.u.). However, there was no difference in the total or percentage of platelet-derived (CD41+) microvesicles between any treatment group at both 6 and 24 hours.
Conclusion: Following traumatic brain injury, amitriptyline decreased platelet aggregability and increased contribution to clot in a manner similar to aspirin. The effect of amitriptyline on platelet function reflects a possible role of acid sphingomyelinase in the hypercoagulability observed following injury and suggests sphingolipid metabolism as a novel target for multimodal VTE chemoprophylaxis. Additionally, inhibition of platelet reactivity may be an underappreciated benefit of low molecular weight heparins, such as enoxaparin, compared to unfractionated heparin use.
