Platelet Function Changes in a Time-Dependent Manner Following Traumatic Brain Injury in a Murine Model

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Traumatic brain injury (TBI) results in systemic changes in coagulation and inflammation that contribute to post-traumatic morbidity and mortality. The potential interaction of platelets and pro-inflammatory cytokines in the modulation of coagulation, microthrombosis, and venous thromboembolic events after moderate TBI (TBI) has not been determined. Using a murine model, we hypothesized 1) that the degree of platelet-induced coagulation varies depending on the platelet aggregation agonist 2) platelet-induced coagulation changes in a time-dependent manner following TBI, and 3) changes in platelet-induced coagulation are mirrored by changes in the levels of circulating pro-inflammatory cytokines. An established weight-drop model was used to induce TBI in anesthetized mice. Blood samples were collected at intervals after injury for measurements of platelet count, serum fibrinogen, pro-inflammatory cytokines, and determination of soluble P-selectin levels. Thromboelastometry was used to evaluate changes in hemostasis. Platelet function was determined using whole blood impedance aggregometry. Ten minutes following TBI, ADP-induced platelet aggregation decreased as measured by platelet aggregometry. Despite no changes in platelet counts and serum fibrinogen, platelet aggregation, pro-inflammatory cytokines, and soluble P-selectin were increased at 6 hours after TBI. ROTEM demonstrated increased maximal clot firmness at 6 hours. Platelet function and coagulability returned to baseline levels 24 hours following head injury. Our data demonstrate that after TBI, acute platelet dysfunction occurs followed by rebound platelet hyperaggregation. Alterations in post-TBI platelet aggregation are reflected in whole blood thromboelastometry and are temporally associated with the systemic pro-inflammatory response.

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