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Temporal aspects of onion-induced antiplatelet activity
Karen S Osmont1, Christina R Arnt, Irwin L Goldman
1Department of Horticulture, University of Wisconsin-Madison, 1575 Linden Drive, Madison, WI 53706, USA.
Abstract:
Organosulfur compounds in onion extracts are formed following the lysis of the S-alk(en)yl-L-cysteine sulfoxides by alliinase. These compounds inhibit the aggregation of human blood platelets and offer the potential for positive cardiovascular health benefits. An experiment was designed to examine temporal and temperature effects on onion-induced antiplatelet activity. Platelet aggregation is induced by various agonists, including ADP, collagen, and thrombin. Unexpectedly, all freshly-juiced onion extracts (ca. 5 minutes post-juicing) appeared to exhibit both an agonist-free aggregation peak (AFP) and a platelet inhibitory peak (PIP) characteristic of inhibition of platelet aggregation. The AFP was minimal by 30 minutes and dissipated in all treatments by 120 minutes, while the PIP increased as onion extracts aged and did not change after 30 minutes at 25 degrees C. This finding confirms the observation that the in vitro platelet inhibitory activity of onion organosulfur compounds is time dependent. Freshly-prepared onion extracts were incubated with the ADP scavenger enzyme apyrase (E.C. 3.6.1.5). AFPs were abolished in apyrase-treated extracts, suggesting that this response may have been due to free ADP in onion extracts, although an amount of ADP required to generate such a response would be unexpected in onion extracts. In addition, platelet aggregates were not observed in the AFP, suggesting this response may be associated with changes in light transmission through platelet rich plasma that are not associated with platelet aggregation. Artifacts of analysis are, therefore, possible when assessing onion-induced antiplatelet activity with freshly-juiced extracts. Temporal formation of platelet-inhibiting organosulfur compounds should be taken into account during both in vitro and in vivo assessment of onion-induced antiplatelet activity.
Insights
Onion extracts show time-dependent antiplatelet activity, with fresh extracts exhibiting artifacts that dissipate over time. Aged extracts demonstrate consistent inhibition of platelet aggregation, highlighting the importance of timing in research.
Area of Science:
- Biochemistry
- Pharmacology
- Food Science
Background:
- Organosulfur compounds in onions, derived from S-alk(en)yl-L-cysteine sulfoxides, possess antiplatelet properties.
- These compounds offer potential cardiovascular health benefits by inhibiting human blood platelet aggregation.
Purpose of the Study:
- To investigate the temporal and temperature effects on the antiplatelet activity of onion extracts.
- To understand the formation and stability of active compounds responsible for onion's effects on platelets.
Main Methods:
- Onion extracts were prepared and their antiplatelet activity assessed at various time points post-juicing.
- Experiments involved inducing platelet aggregation with agonists like ADP and measuring aggregation.
- Apyrase enzyme was used to investigate the role of free ADP in observed effects.
Main Results:
- Freshly-juiced onion extracts showed an agonist-free aggregation peak (AFP) and a platelet inhibitory peak (PIP).
- The AFP diminished within 120 minutes, while the PIP increased with extract aging, stabilizing after 30 minutes at 25°C.
- Apyrase abolished the AFP, suggesting it might be due to free ADP or an analytical artifact.
Conclusions:
- The in vitro antiplatelet activity of onion organosulfur compounds is time-dependent.
- Analytical artifacts can occur with freshly-juiced onion extracts, impacting the assessment of antiplatelet activity.
- Temporal considerations are crucial for accurate in vitro and in vivo evaluation of onion's cardiovascular benefits.