Hemoglobin-based oxygen carriers promote systemic hyperfibrinolysis that is both dependent and independent of plasmin

Abstract

<div class="section"> <a class="named-anchor" id="S1"> <!-- named anchor --> </a> <h5 class="section-title" id="d9123344e190">Background</h5> <p id="P1">Hyperfibrinolysis plays an integral role in the genesis of trauma-induced coagulopathy (TIC). Recent data demonstrates that red blood cell (RBC) lysis promotes fibrinolysis; however, the mechanism is unclear. Hemoglobin-based oxygen carriers (HBOC) have been developed for resuscitation and have been associated with coagulopathy. We hypothesize that replacement of whole blood (WB) using an HBOC results in a coagulopathy due to the presence of free hemoglobin. </p> </div><div class="section"> <a class="named-anchor" id="S2"> <!-- named anchor --> </a> <h5 class="section-title" id="d9123344e195">Materials and Methods</h5> <p id="P2">Whole blood was sampled from healthy donors (n=6). The clotting profile of each citrated sample was evaluated using native thrombelastography (TEG). Serial titrations were performed using both HBOC (Polyheme) and normal saline (NS) (5%, 25%, and 50%) and evaluated both with and without a 75 ng/microliter tissue-plasminogen activator (tPA) challenge. Tranexamic acid (TXA) was added to inhibit plasmin dependent fibrinolysis. Fibrinolysis was measured and recorded as LY30, the percentage of clot lysis at 30 minutes after maximal clot strength. Dilution of WB with NS or HBOC was correlated using LY30 via Spearman Rho coefficients. Groups were also compared using a Friedman test and post-hoc analysis with a Bonferroni adjustment. </p> </div><div class="section"> <a class="named-anchor" id="S3"> <!-- named anchor --> </a> <h5 class="section-title" id="d9123344e200">Results</h5> <p id="P3">TPA provoked fibrinolysis was enhanced by both HBOC (median LY30 at 5%, 25%, 50% titrations: 11%, 21%, 44%; Spearman=0.94; p&lt;0.001) and NS (11%, 28%, 58%; Spearman=0.790; p&lt;0.001). However, HBOC also enhanced fibrinolysis without the addition of tPA (1%, 4%, 5%; Spearman=0.735; p=0.001) and NS did not (1%, 2%, 1%; r=0.300; p=0.186.Moreover, addition of TXA did not alter or inhibit this fibrinolysis (WB vs 50% HBOC: 1.8% vs 5.7%, p=0.04). There was no significant difference in fibrinolysis of HBOC with or without TXA (50% HBOC vs 50% HBOC +TXA: 5.6% vs 5.7%, p=0.92). Additionally, the increased fibrinolysis seen with NS was reversed when TXA was present (WB vs 50% NS: 1.8% vs 1.7%, p=1.0). </p> </div><div class="section"> <a class="named-anchor" id="S4"> <!-- named anchor --> </a> <h5 class="section-title" id="d9123344e205">Conclusion</h5> <p id="P4">HBOCs enhance fibrinolysis both with and without addition of tPA; moreover, this mechanism is independent of plasmin as the phenomenon persists in the presence of TXA. Our findings indicate the hemoglobin molecule or its components stimulate fibrinolysis by both tPA-dependent and innate mechanisms. </p> </div>