The Effects of vanilloid-like agents on platelet aggregation

Capsaicin, the 'hot' principle found in chilli, and other vanilloids exert their effects on neuronal cells through activation of transient receptor potential vanilloid 1 (TRPV1). TRPV1 is widely distributed in neuronal and non-neuronal cells. It has been proposed that consumption of vanilloid-like agents, including capsaicinoids, inhibits platelet aggregation and may protect against the development of cardiovascular disease. The aim of this study was to investigate the effects of a range of vanilloid-like agents on in vitro platelet aggregation. Venous blood was collected from healthy subjects who avoided antiplatelet medications and dietary chilli for at least 10 and 2 days, respectively. Collagen (4 and 8 ˜í¬¿g/mL), ADP (10 and 5 ˜í¬¿M) and arachidonic acid (AA) (300 and 400 mg/mL) -induced platelet aggregation was determined using platelet rich plasma (PRP; \\(250x10^9L\\)) in the absence and presence of the capsaicinoids [capsaicin and dihydrocapsaicin (DHC)] and the endocannabinoid/endovanilloid agents [Noleoyldopamine (OLDA) and N-arachidonoyl-dopamine e (NADA)]. %Maximum aggregation (%Max), % area under curve (%AUC) and slope of platelet aggregation were determined. Platelet lactate dehydrogenase (LDH), which is released rapidly after cell membrane damage, was investigated to determine the direct toxic effects of these agents on platelets. Platelet factor 4 (PF4) and ˜í‚â§-thromboglobulin (˜í‚â§-TG) release were examined to determine the effects of vanilloids on alpha granule release. Finally, the effects of TRPV1 antagonist (SB-452533) on capsaicin- and OLDA-mediated inhibition of ADP-induced platelet aggregation were investigated. ADP-induced (5 ˜í¬¿M) platelet aggregation was inhibited in a concentration-dependent manner by capsaicin (%Max, mean ¬¨¬±SEM; 0 vs 100 ˜í¬¿M, 83.8¬¨¬±0.9% vs 45.2¬¨¬±2.4%, n=6, p>0.001); OLDA (0 vs 100 ˜í¬¿M, 71.6¬¨¬±8.2% vs 9.4¬¨¬±1.4%, n=4, p<0.001); and NADA (0 vs 100 ˜í¬¿M, 71.5¬¨¬±5.9% vs 38.2¬¨¬±1.4%, n=4, p<0.008). Similar results were observed using 10 ˜í¬¿M ADP. OLDA and NADA, but not capsaicin and DHC, inhibited platelet aggregation induced by 4˜í¬¿g/mL collagen: OLDA (Max%, 0 vs 100 ˜í¬¿M, 89.3¬¨¬±1.4% vs 45.5¬¨¬±12.5%, p<0.001); and NADA (0 vs 100 ˜í¬¿M, 87.7¬¨¬±0.8% vs 28.5¬¨¬±8.2%, p<0.001). AA-induced (300 mg/mL) aggregation was inhibited in a concentration-dependent manner by capsaicin (Max%, 0 vs 100 ˜í¬¿M, 89.6¬¨¬±0.9% vs 11¬¨¬±0.8%, p<0.001); DHC (0 vs 100 ˜í¬¿M, 88.3¬¨¬±2.1% vs 18.7¬¨¬±6.9%, p<0.001); and NADA (0 vs 100 ˜í¬¿M, 84¬¨¬±1.8% vs 21.9¬¨¬±4.7%, p<0.001). Similar results were observed using 400mg/mL AA. The inhibition of platelet aggregation by all agents was not due to direct toxic effects as LDH release from platelets was unaffected by any of the vanilloids. SB-452533 did not inhibit the effects of OLDA (SB-45253; Max 0 vs 10˜í¬¿M, 55.9¬¨¬±2.1% vs 58.4¬¨¬±1.37%) and capsaicin (SB-45253; Max 0 vs 10˜í¬¿M, 65.15¬¨¬±0.44% vs 65.55¬¨¬±1%) on platelet aggregation, suggesting that inhibition of ADP-induced aggregation is not TRPV1 mediated. ADP-stimulated PF4 release from platelets was impaired by capsaicin, DHC and OLDA whereas NADA enhanced ADP-stimulated PF4 release. Furthermore, OLDA and capsaicin impaired the release of ˜í‚â§-TG from ADP-stimulated platelets. The present study using human platelet shows that capsaicin, DHC, OLDA and NADA inhibit in vitro aggregation. The inhibitory effects of vanilloids are not TRPV1 mediated and not due to a direct toxic effect on platelets. Vanilloids may inhibit platelet aggregation by interfering with granule release, although further investigation of this possibility is warranted.