The antiplatelet activity of rutaecarpine, an alkaloid isolated from Evodia rutaecarpa, is mediated through inhibition of phospholipase C

In this study, the mechanism involved in the antiplatelet activity of rutaecarpine in human platelet suspensions was investigated. In platelet suspensions (4.5 x 10(8)/ml), rutaecarpine (100 and 200 mu M) did not influence the binding of FITC-triflavin to platelet glycoprotein IIb/IIIa complex. Additionally, rutaecarpine (200 mu M) did not significantly change the fluorescence of platelet membrane labeled with diphenylhexatriene (DPH), On the other hand, rutaecarpine (50 and 100 mu M) dose-dependently inhibited the increase in intracellular free Ca2+ of Fura 2-AM loaded platelets stimulated by collagen. Moreover, rutaecarpine (100 and 200 mu M) did not significantly affect the thromboxane synthetase activity of aspirin-treated platelet microsomes, Furthermore, retaecarpine (100 and 200 mu M) significantly inhibited [H-3]arachidonic acid released in collagen-activated platelets but not in unactivated-platelets. Nitric oxide (NO) production in human platelets was measured by a chemiluminesence detection method in this study. Rutaecarpine (100 and 200 mu M) did not significantly affect nitrate production in collagen (10 mu g/ml)- induced human platelet aggregation. On the other hand, various concentrations of rutaecarpine (50, 100, and 200 mu M) dose-dependently inhibited [H-3]inositol monophosphate formation stimulated by collagen (10 mu g/ml) in [H-3] myoinositol-loaded platelets at different incubation times (1, 2, 3, and 5 minutes). It is concluded that the antiplatelet activity of rutaecarpine may possibly be due to the inhibition of phospholipase C activity, leading to reduce phosphoinositide breakdown, followed by the inhibition of thromboxane A(2) formation, and then inhibition of [Ca2+]i mobilization of platelet aggregation stimulated by agonists. (C) 1998 Elsevier Science Ltd.