Inhibition of platelet activation by quinones isolated from Auxemma oncocalyx Taub.

The present work explored the anti-platelet effect produced by the quinone fractions (17.8, 35.7 and 71.4 microg/ml) isolated from the heartwood of Auxemma oncocalyx Taub. Our results show that the quinone fraction (QF) is a reversible and concentration-dependent inhibitor of human platelet aggregation induced by ADP, arachidonic acid (AA), collagen and thrombin. Besides, the QF effect was significantly potentiated after its association with aspirin or imidazole, and in this case, the AA-induced platelet aggregation was completely blocked. The addition of QF to L-arginine caused a small but significant increase in the percentage of platelet inhibition (13%) only when compared to QF alone. Finally, the addition of QF to pentoxifylline, a known phosphodiesterase inhibitor, resulted in significant potentiation (43% inhibition) of the antiplatelet effects seen with QF (9.7%) or PTX (10%) alone. Although QF presented an antiplatelet effect, it caused a significant decrease in bleeding time, manifested 3 h after oral (100 or 200 mg/Kg) or 1 and 3 h after intraperitonial (30 mg/Kg) administration. In conclusion. QF possibly acts through a combined cyclo-oxygenase and TxA2 synthase inhibition. Besides, QF also increases platelets cAMP levels which also contributes to its anti-aggregatory effects.