Synergistic inhibitory effect of capsaicin and dihydrocapsaicin on in vitro platelet aggregation and thromboxane formation

Capsaicinoids, including capsaicin (CAP) and dihydrocapsaicin (DHC), the pungent principles of pepper fruits, individually inhibit in-vitro platelet aggregation. However, their effects, when present together, are not known. The aims of this study were to compare the effects of CAP and DHC alone, and in combination in the ratio that they are found in chilies (∼60% CAP : 40% DHC), on in-vitro platelet aggregation, platelet count and thromboxane B2 (TXB2) formation. The effects of 12.5 and 6.25 μmol/l CAP and DHC individually, and in combination (CAP : DHC, 60 : 40) on arachidonic acid-induced, ADP-induced and collagen-induced aggregation, were investigated. Platelet count was determined preincubation and postincubation with CAP and DHC and in combination. TXB2 formation from platelets treated with arachidonic acid in the absence and presence of CAP and DHC individually, and in combination, was measured. Compared with control, CAP and DHC (12.5 μmol/l) inhibited arachidonic acid-induced aggregation by 23.2 and 25.3%, respectively (both P < 0.01). In combination, CAP and DHC exhibited further inhibition in arachidonic acid-induced aggregation (CAP : DHC, 3.75 : 2.5 μmol/l, 36.5%, P = 0.01; 7.5 : 5 μmol/l, 57.5%, P < 0.001), compared with control. Incubation of platelets with caspaicinoids did not significantly affect the platelet count. In addition, the CAP : DHC (7.5 : 5 μmol/l) combination significantly inhibited (P < 0.001) TXB2 formation, compared with the individual capsaicinoids. Capsaicinoids had no effect ADP-induced or collagen-induced aggregation. The combination of CAP and DHC produces a significantly greater inhibitory effect on arachidonic acid-induced platelet aggregation and subsequent TXB2 formation, compared with the individual capsaicinoids.