Antithrombotic effect of repeated doses of the ethanolic extract of local olive (Olea europaea L.) leaves in rabbits

The incidence of thromboembolic diseases is increasing, and they are a major cause of mortality and morbidity worldwide. Mediterranean diet is known for its high content of olive products, especially olive oil, which has known cardiovascular health benefits, including those on blood pressure, cholesterol level, and thrombogenesis. All previous animal and clinical studies investigating the beneficial antithrombotic effects of olives have focused on olive oil and a few on olive leaves (OLEs). In this study, the ethanolic extract of OLE was evaluated for its antithrombotic activity in the rabbit model of thrombosis induced by ligature of the vena cava and intravenous administration of tissue thromboplastin. Pre-treatment with 100 or 200 mg/kg per day of the ethanolic extract for 8 weeks significantly prolonged the prothrombin time (PT) in comparison to the control group (12.10 +/- 0.35 sec and 14.38 +/- 0.29 sec vs. 10.8 +/- 0.32 sec, p<0.05 and 0.001, respectively). In comparison to the control group, the same doses had no statistically significant effect on thrombus weight (16.85 +/- 0.67 mg, 16.32 +/- 0.35 mg, and 17.81 +/- 0.75 mg; p = 0.18 and 0.06) or on activated partial thromboplastin time (APTT) (19.17 +/- 0.33 sec, 19.12 +/- 0.73 sec, and 18.97 +/- 0.41 sec; p = 0.36 and 0.43, respectively). One important finding in this study concerns thrombus morphology. In the extract treatment groups, the thrombus was filament-like and did not adhere to blood vessel walls, whereas in the control group the thrombus was thick and almost completely occluded the vein. Therefore, these results suggest that OLE ethanolic extract can modify the extrinsic coagulation pathway as evidenced by the prolongation of PT and changes in thrombus morphology, enough to justify further research to evaluate its possible antithrombotic effects.