The CRASH-26 and MATTERs7 clinical studies revealed that, when TXA is administered within 3 hours after injury, mortality is reduced by up to 20%.8 Recent reanalysis of the clinical data further showed that the survival benefit of TXA decreased by 10% for every 15 minutes of delayed administration, with no benefit obtained after 3 hours.9 This lack of efficacy outside of the “3-hour window” has been associated with the upregulation of plasma uPA postinjury.6,10,11
We have previously observed that a very high concentration (∼25 mM) of TXA inhibits Plm activity via binding to the primary catalytic (S1) pocket of the enzyme.12 However, because of the low affinity of TXA for Plm, we do not anticipate that TXA functions as a Plm inhibitor during clinical use.12 However, given these findings, we investigated whether TXA may have an inhibitory effect on other proteases in the Plg-activation system. Unexpectedly, our results revealed that TXA attenuates uPA activity with an inhibitory constant (Ki) of 2 mM. In contrast, similar efficacy is not observed in the presence of ε-aminocaproic acid (EACA; an alternative drug to TXA).
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