Temporal aspects of onion-induced antiplatelet activity

Abstract

Organosulfur compounds in onion extracts are formed following thelysis of the S-alk(en)yl-L-cysteine sulfoxides by alliinase. Thesecompounds inhibit the aggregation of human blood platelets and offer thepotential for positive cardiovascular health benefits. An experiment wasdesigned to examine temporal and temperature effects on onion-inducedantiplatelet activity. Platelet aggregation is induced by various agonists,including ADP, collagen, and thrombin. Unexpectedly, all freshly-juicedonion extracts (ca. 5 minutes post-juicing) appeared to exhibit both anagonist-free aggregation peak (AFP) and a platelet inhibitory peak (PIP)characteristic of inhibition of platelet aggregation. The AFP was minimalby 30 minutes and dissipated in all treatments by 120 minutes, whilethe PIP increased as onion extracts aged and did not change after 30minutes at 25 ^°C. This finding confirms the observation that the in vitro platelet inhibitory activity of onion organosulfur compounds istime dependent. Freshly-prepared onion extracts were incubated with theADP scavenger enzyme apyrase (E.C. 3.6.1.5). AFPs were abolished inapyrase-treated extracts, suggesting that this response may have been dueto free ADP in onion extracts, although an amount of ADP required togenerate such a response would be unexpected in onion extracts. Inaddition, platelet aggregates were not observed in the AFP, suggesting thisresponse may be associated with changes in light transmission throughplatelet rich plasma that are not associated with platelet aggregation.Artifacts of analysis are, therefore, possible when assessing onion-inducedantiplatelet activity with freshly-juiced extracts. Temporal formation ofplatelet-inhibiting organosulfur compounds should be taken into accountduring both in vitro and in vivo assessment of onion-inducedantiplatelet activity.