Inhibition of Cyclic AMP Phosphodiesterase and Blockage of Arachidonate Metabolism by Antiplatelet Principles from the Seed Hulls of Arachis Hypogaea L.

The antiplatelet activity of eight principles isolated from the seed hulls of Arachis hypogaea L. (A. hypogaea) was determined in washed rabbit platelets. Six flavonoids including luteolin, 8-iso- pentenyl luteolin, eriodictyol, chrysoeriol, 8-isopentenyl chrysoeriol and 4', 5-dihydroxy-2”, 2”- dimethylpyrano[5”,6”:7,8]flavone (AHO6) inhibited platelet aggregation induced by arachidonic acid (AA), collagen, U46619, ADP, platelet-activating factor (PAF) and thrombin in a concentration-dependent manner. These flavonoids were most potent against AA-mediated platelet activation. The flavonoids not only suppressed the elevation of intracellular calcium ([Ca(superscript 2+)]i) but also increased cyclic AMP (cAMP) levels in platelets. Concomitantly, the five flavones degraded exogenously added cAMP as cilostamide did in platelet lysates containing adenylate cyclase inhibitor. But they didn't mimic forskolin to convert ATP to cAMP in platelet lysates containing cAMP phosphodiesterase inhibitor. These results indicate that the flavones act as cAMP phosphodiesterase inhibitors, which allows accumulation of intra-platelet cAMP and consequently represses increasing of [Ca(superscript 2+)]i) induced by the aggregation agonists. Furthermore, these flavonoids also affected AA-metabolism-related enzymes. 8-Isopentenyl chrysoeriol decreased malondialdehyde (MDA) and thromboxane B2(TXB2) formation but increased prostaglandin (PG)E2 and F(superscript 2a) formation from AA indicating its inhibitory activity of thromboxane synthase. The other five flavonoids all inhibited the activity of cyclooxygenase, decreasing AA-metabolites including MDA, TXB2, PGE2 and PGF(superscript 2a).