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Studies on murine embryo-derived platelet-activating factor (EPAF)
L M Adamson1, B Podsiadly, Y C Smart
1Department of Biological Sciences and Discipline of Surgical Science, University of Newcastle, New South Wales, Australia.
Abstract:
Studies were carried out using the splenectomized mouse bioassay (SMB) to investigate the nature of embryo-derived platelet-activating factor (EPAF) and its relationship to synthetic platelet activating factor (PAF). While both C16-PAF and embryo conditioned media (ECM) induced a significant platelet decline in the SMB at 15 min postinjection, C18-PAF induced a similar effect at 30 min postinjection. The degree of EPAF activity in ECM was not altered with increasing embryo number from 2 to 40/ml of media. In contrast, PAF (C16/C18 mixture) induced a linear increase in activity with increasing concentration, leading to lethal effects at high concentrations. While EPAF activity was not significantly altered when ECM was diluted 1/1,000, PAF activity was abolished at 1/10 dilution. EPAF in ECM was not inactivated by mouse plasma; however, lipid extracted ECM, like PAF, underwent rapid inactivation in the presence of plasma. Aggregometer studies using horse platelets showed that ECM and lipid-extracted ECM were unable to induce platelet aggregation, while thin-layer chromatography (TLC) purified ECM (Rf 0.23) successfully aggregated horse platelets in vitro. Results suggested that EPAF and PAF are not homologous. EPAF might consist of PAF bound to a regulatory carrier molecule and appears to be associated with EPAF-inhibitor substance(s) in ECM.
Insights
Embryo-derived platelet-activating factor (EPAF) differs from synthetic platelet-activating factor (PAF). EPAF is more stable and does not aggregate platelets, suggesting it is not homologous to PAF.
Area of Science:
- Biochemistry
- Immunology
- Hematology
Background:
- Platelet-activating factor (PAF) is a potent lipid mediator involved in various physiological and pathological processes.
- The existence and nature of embryo-derived platelet-activating factor (EPAF) remain less understood, particularly its relationship to synthetic PAF.
Purpose of the Study:
- To investigate the characteristics of embryo-derived platelet-activating factor (EPAF) using the splenectomized mouse bioassay (SMB).
- To compare the properties of EPAF with synthetic platelet activating factor (PAF) and determine their relationship.
Main Methods:
- Splenectomized mouse bioassay (SMB) to assess platelet-activating effects.
- Platelet aggregation studies using horse platelets.
- Thin-layer chromatography (TLC) for purification and characterization.
- Plasma inactivation assays.
Main Results:
- Both C16-PAF and embryo conditioned media (ECM) caused significant platelet decline in SMB at 15 min, while C18-PAF acted at 30 min.
- EPAF activity in ECM was independent of embryo number, unlike PAF which showed linear increase with concentration.
- EPAF was stable in mouse plasma and at high dilutions, whereas PAF activity was abolished at low dilutions and rapidly inactivated by plasma.
- ECM and lipid-extracted ECM did not induce platelet aggregation in vitro, but purified EPAF did.
Conclusions:
- EPAF and synthetic PAF are not homologous molecules.
- EPAF may involve PAF bound to a regulatory carrier molecule and is associated with inhibitory substances in ECM.
- These findings differentiate EPAF from PAF, suggesting distinct biological roles and mechanisms.