Antithrombotic and antiplatelet activities of orientin in vitro and in vivo

Vaccinium bracteatum Thunb. is commonly used in staining and cooking rice. However, there are limited data regarding its active components and pharmacological effects that underlie its traditional use. Two flavonoid C-glycosyl compounds (orientin and isoorientin) found in V. bracteatum Thunb. are known for their antioxidant activity. Here, the anticoagulant activity of orientin and isoorientin was examined by monitoring the activated partial thromboplastin time (aPTT), prothrombin time (PT), and the thrombin and activated factor X (FXa) activity. Treatment with orientin and isoorientin prolonged the aPTT and PT and inhibited the thrombin and FXa activity and production in human umbilical vein endothelial cells (HUVECs). Furthermore, orientin and isoorientin inhibited thrombin-catalyzed fibrin polymerization and platelet aggregation. In exploring the mechanism underlying anti-platelet aggregation, we found that orientin and isoorientin specifically prevented protein kinase C (PKC) activation and calcium mobilization. Orientin and isoorientin also elicited anticoagulant effects in mice. In addition, treatment with orientin and isoorientin significantly decreased the plasminogen activator inhibitor-1 (PAI-1) to tissue plasminogen activator (t-PA) ratio. Collectively, foods containing orientin and isoorientin possess antithrombotic activity and may be used in preventing thrombus formation and improving blood circulation.