Tsutomu Kamiyama

Tetrafibricin: a nonpeptidic fibrinogen receptor inhibitor from Streptomyces neyagawaensis. (II). Its antiplatelet activities.

Tetrafibricin; a nonpeptidic fibrinogen inhibitor from microbial origin, showed potent antiaggregation activities on human platelet aggregation induced by either ADP, thrombin or collagen (IC50s = 5.6, 7.6 and 11 microM, respectively) in platelet rich plasma. The ability to inhibit aggregation in platelets treated with chymotrypsin confirmed the GPIIb/IIIa blockage of tetrafibricin. Tetrafibricin blocked the release of serotonin induced by ADP but it did not block the release reaction induced by thrombin. When added to platelets formerly aggregated with ADP, tetrafibricin caused rapid and complete deaggregation. As for the selectivity among other Arg-Gly-Asp -dependent integrins, tetrafibricin seems to be more specific for glycoprotein (GP) IIb/IIIa than RGDS is. This is because it had no effect on adhesion of bovine aortic endothelial cells to RGD-containing proteins. Tetrafibricin is the first nonpeptidic fibrinogen receptor inhibitor that may be valuable for the study on platelet aggregation inhibitors.

Tetrafibricin: A nonpeptidic fibrinogen receptor inhibitor from Streptomyces neyagawaensis (I) its GPIIB/IIIA blockage on solid phase binding assay

Tetrafibricin is a novel nonpeptidic fibrinogen receptor inhibitor isolated from Streptomyces neyagawaensis NR0577. Its competitive and selective fibrinogen receptor blockage was demonstrated in this study. Tetrafibricin competitively inhibited (Ki = 9.9 nM) the binding of biotinylated fibrinogen to purified active glycoprotein (GP) IIb/IIIa immobilized on plastic plate. When RGDS and tetrafibricin were added in combination, the inhibition was additive. The binding of other RGD-containing proteins, fibronectin and von Willebrand factor, to active GPIIb/IIIa were also completely inhibited by tetrafibricin. The fact that tetrafibricin did not inhibit the binding of von Willebrand factor to GPIb/IX indicates the specific blockage of tetrafibricin for GPIIb/IIIa. Fibrinogen receptor inhibition of tetrafibricin was also confirmed by its ability to inhibit 125I-fibrinogen binding to platelets stimulated with ADP. Because of its competitiveness and specificity, tetrafibricin can be used in a new structural model for the design of fibrinogen receptor inhibitors.