Inhibition of the Activities of α2-Plasmin Inhibitor (PI) and CĪ Inhibitor (CĪ-Inh by the Synthetic Fibrinolytic Agent, 3-Hydroxypropyl Flufenamide (Flu-HPA)
Flu-HPA is one of a series of flufenamic acid derivatives that enhances plasminogen-de-pendent clot lysis in vitro. Studies of possible mechanisms of action of Flu-HPA were undertaken. The influence of Flu-HPA on the inhibition of purified plasmin by purified PI was studied. PI activity was assessed by its inhibition of the cleavage of the tripeptide S-2251(H-D-Val-Leu-Lys-pNA) by plasmin. Flu-HPA was dissolved in DMF or in n-ethanol and preincubated with PI before addition of plasmin. At FIu-HPA concentrations greater than ImM and up to 60mM, the inhibitory activity of PI was totally lost. The inhibitory effect of normal human plasma on plasmin was also completely abolished at concentrations of Flu-HPA between 2.5 and 40mM. The effect of Flu-HPA on the inhibition of purified plasma kallikrein by purified CĪ-Inh was also studied. CĪ-Inh activity was measured by its inhibition of cleavage of the tripeptide Bz-Pro-Phe-Arg-pNA by kallikrein. When FIu-HPA, dissolved in DMF or in methanol, was preincubated with CĪ-lnh, a concentration dependent inhibition of CĪ-Inh activity was observed. CĪ-Inh activity was abolished by concentrations of Flu-HPA greater than ImM. Flu-HPA also inhibited the activity of CĪ-Inh on purified Factor XIIa. These observations suggest that this flufenamic acid derivative may enhance fibrinolysis not only by inhabiting PI activity but also by decreasing the inactivation of plasminogen activators by CĪ-Inh.