Abstract

Plant-derived flavonoids may modulate both coagulation proteases and platelet activation, but integrated evidence across the platelet-coagulation interface remains limited. This study evaluated a phytochemically standardized scutellarin-rich fraction (SRF) using complementary plasma, platelet, whole-blood, pharmacodynamic, and ex vivo thrombosis-associated assays. SRF was isolated from the aerial parts of Inula salicina L. and characterized as a scutellarin-dominant flavonoid fraction. Citrated plasma was analyzed for thrombin time (TT), plasma recalcification time (PRT), prothrombin time (PT), and activated partial thromboplastin time (APTT). Platelet-rich plasma was examined by adenosine diphosphate (ADP)-induced aggregometry and Fura-2/AM calcium imaging. Rat thromboelastography, serial clotting-time monitoring, and FeCl3 carotid injury-associated ex vivo plasma assays were used to assess systemic and injury-associated responses. SRF prolonged PRT concentration-dependently in vitro (10-100 µM) and increased TT, PT, and APTT, indicating a broad plasma hypocoagulant phenotype. It also inhibited ADP-induced platelet aggregation, nearly abolished the second aggregation phase, and attenuated agonist-evoked intracellular Ca2+ signaling without behaving as a simple extracellular calcium chelator. In rats, SRF delayed thromboelastographic clot initiation and slowed clot development. Serial pharmacodynamic assays showed rapid route-dependent clotting-time prolongation. In the FeCl3 series, oral SRF dose-dependently shifted the injury-associated hypercoagulable profile toward anticoagulation. These findings suggest that SRF exhibits integrated anticoagulant and antiplatelet activity at the platelet-coagulation interface, consistent with modulation of thrombin-fibrin conversion, membrane-dependent coagulation complex assembly, and calcium-dependent platelet amplification.

Key words: Anticoagulant activity, Ferric chloride, Flavonoids, Platelet aggregation, Scutellarin-rich fraction, Thrombosis