Effects of flavonoids from licorice roots ( Glycyrrhiza inflata Bat.) On arachidonic acid metabolism and aggregation in human platelets

The effects of six flavonoids isolated from Sinkiang Licorice roots (lichochalcones A and B, isoliquiritigenin, isoliquiritin, liquiritigenin and liquiritin) on arachidonate metabolism and aggregation in human platelets were studied. Licochalcones A and B at concentrations of 10 −5 M to 10 −3 M inhibited the formation of 12‐hydroxy‐5,8,10‐heptadecatrienoic acid (HHT) and thromboxane B 2 (TXB 2 ), does‐dependently. Furthermore, isoliquiritigenin and liquiritigenin at higher concentrations (10 −4 M–10 −3 M) inhibited the formation of HHT and TXB 2 , while they increased the formation of 12‐hydroxy‐5,8,10,14‐eicosatetraenoic acid (12‐HETE). However, isoliquiritin and liquiritin had no effect on arachidonate metabolism. Licochalcones A and B inhibited thrombin‐induced platelet aggregation at concentrations of 2 × 10 −5 M to 2 × 10 −4 M. Isoliquiritigenin, liquiritigenin, isoliquiritin and liquiritin had no effects on the thrombin‐induced aggregation. To clarify the inhibitory effects of flavonoids in licorice roots on the formation of HHT and TXB 2 and thrombin‐induced aggregation, we studied the effects of flavonoids on cytosolic free calcium concentrations ([Ca 2+ ]i) induced by thrombin. The results showed that licochalcones A and B inhibited the elevation of [Ca 2+ ]i induced by thrombin, dose‐dependently.