An Anti-plasmin Inhibitor, Eckol, Isolated from the Brown Alga Ecklonia kurome OKAMURA

The biological activities of eckol, a novel phlorotannin with a dibenzo-β-dioxine skeleton, were examined. Eckol inhibited the antiplasmin activity of a2-plasmin inhibitor very efficiently (IC50; 1.6 μg/ml) as well as those of α2-macroglobulin and -antitrypsin. However, its inhibitory effect on the antithrombin III-heparin complex was very weak. Eckol also showed inhibitory activity on thrombin (IC50; 12 μg/ml), but not on plasmin. Its inhibitory activity was reduced in whole human plasma, but at concentrations of above 200 μg/ml it enhanced urokinase-induced fibrinolysis in human plasma. Studies on the inhibitory spectra of several derivatives of eckol showed that the dibenzo-l,4-dioxane skeleton was necessary for inhibition of plasmin inhibitor. These observations suggest that eckol or its derivatives may be useful clinically for potentiating thrombolytic activity.