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Platelet aggregating substance from mononuclear leukocytes
Abstract:
Human peripheral blood mononuclear leukocytes (ML) in suspension stimulated with arachidonic acid (AA) were able to induce platelet aggregation. Shape change followed by first and second wave aggregation was the pattern of the platelet response. ML not treated with AA did not induce platelet aggregation nor did AA done at the concentration employed. The aggregating activity was not due to the ML presence, since cell-free supernatants of ML stimulated with AA induced similar platelet aggregation as the whole suspension. Aspirin incubated with ML-AA produced 65% reduction of the above aggregatory activity described while 38% and 45% reduction was obtained when ML-AA was incubated with 5, 8, 11, 14 eicosatetraynoic acid (ETYA) and nordihydroguaiaretic acid (NDGA). Complete platelet cyclooxygenase integrity was necessary to obtain the second wave of aggregation induced by ML-AA, while this was not required for the first wave response. We propose that ML-AA are able to produce a platelet activating substance(s) derived from AA metabolism involving cyclo and lipoxygenase actions. It is unlikely that this substance(s) is a hydroperoxyfatty acid or thromboxane A2 (TXA2) since it is active for at least two hours once generated.
Insights
Human leukocytes stimulated with arachidonic acid (AA) induce platelet aggregation. This effect involves AA metabolism via cyclooxygenase and lipoxygenase pathways, suggesting novel platelet-activating substances.
Area of Science:
- Immunology
- Biochemistry
- Hematology
Background:
- Human peripheral blood mononuclear leukocytes (ML) can influence platelet function.
- Arachidonic acid (AA) is a precursor to various signaling molecules involved in inflammation and hemostasis.
Purpose of the Study:
- To investigate the ability of AA-stimulated ML to induce platelet aggregation.
- To elucidate the metabolic pathways involved in the generation of platelet-activating substances by ML.
Main Methods:
- Incubation of human peripheral blood mononuclear leukocytes (ML) with arachidonic acid (AA).
- Assessment of platelet aggregation response (shape change, first and second wave aggregation).
- Inhibition studies using aspirin, 5, 8, 11, 14 eicosatetraynoic acid (ETYA), and nordihydroguaiaretic acid (NDGA).
Main Results:
- AA-stimulated ML induced significant platelet aggregation, characterized by shape change and biphasic aggregation.
- Cell-free supernatants from AA-stimulated ML also induced platelet aggregation, indicating secreted mediators.
- Aspirin, ETYA, and NDGA partially inhibited the aggregatory activity, suggesting involvement of cyclooxygenase and lipoxygenase pathways.
- Complete cyclooxygenase integrity was essential for the second wave of aggregation, but not the first.
Conclusions:
- ML stimulated with AA produce platelet-activating substance(s) derived from AA metabolism.
- These mediators likely involve both cyclooxygenase and lipoxygenase pathways.
- The generated substance(s) are not hydroperoxy fatty acids or thromboxane A2, as they remain active for extended periods.