Acetyl eugenol, a component of oil of cloves ( Syzygium aromaticum L.) inhibits aggregation and alters arachidonic acid metabolism in human blood platelets

Abstract

In continuation of our studies with the oil of cloves — a common kitchen spice and a crude drug for home medicine — we have isolated yet another active component identified as acetyl eugenol (AE); the earlier reported active component being eugenol. The isolated material (IM) was found to be a potent platelet inhibitor; IM abolished arachidonate (AA)-induced aggregation at ca. 12 μM, a concentration needed to abolish the second phase of adrenaline-induced aggregation. Chemically synthesized acetyl eugenol showed similar effects on AA- and adrenaline-induced aggregation. A dose-dependent inhibition of collagen-induced aggregation was also observed. AE did not inhibit either calcium ionophore A23187- or thrombin-induced aggregation. Studies on aggregation and ATP release were done using whole blood (WB). AA-induced aggregation in WB was abolished at 3 μg/ml (14.6 μM) which persisted even after doubling the concentration of AA. ATP release was inhibited. Inhibition of aggregation appeared to be mediated by a combination of two effects: reduced formation of thromboxane and increased generation of 12-lipoxygenase product (12-HPETE). These effects were observed by exposing washed platelets to ( 14C)AA or by stimulating AA-labelled platelets with ionophore A23187. Acetyl eugenol inhibited ( 14C)TxB 2 formation in AA-labelled platelets on stimulation with thrombin. AE showed no effect on the incorporation of AA into platelet phospholipids.