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Species-specific variations in the molecular heterogeneity of the platelet-activating factor
Abstract:
The molecular heterogeneity of platelet-activating factor (PAF) synthesized by unstimulated and Ca2+ ionophore (A23187)-stimulated PMN from rat, mouse, and guinea pig and by rat basophilic leukemia (RBL) cells was investigated by gas chromatography-negative ion chemical ionization mass spectrometry. Several molecular species of PAF ranging from C14:0 to C19:0 were detected in all of the cells studied. PAF produced by each cell type exhibited a unique pattern of molecular species distribution. Although C16:0 was the major PAF molecular species of rat PMN and RBL cells representing 96% and 85% of the total PAF, respectively, PAF from mice PMN contained 81% of C16:0, 10% of C18:1, and 6% of C18:0. Alternatively, A23187-stimulated guinea pig PMN yielded PAF molecular species 35% in C16:0, 35% in C17:0, 8% in C18:1, and 3% in C18:0. Small but significant differences in the PAF molecular species distribution of resting and ionophore stimulated cells were also observed. In contrast to the PAF molecular species composition, the precursor 1-O-alkyl-2-acyl-glycero-3-phosphocholine of all the cell types was predominantly hexadecyl (C16:0) alkyl chain in the sn-1 position, representing 60 to 80% of the total 1-O-alkyl-2-acyl-glycero-3-phosphocholine. Thus, these results not only indicate a high degree of selectivity for utilization of precursor substrates for PAF biosynthesis, but also demonstrate that the selectivity is species specific.
Insights
Platelet-activating factor (PAF) molecular species vary significantly across different animal cell types, revealing species-specific synthesis patterns. This research highlights selective precursor utilization in PAF biosynthesis.
Area of Science:
- Biochemistry
- Immunology
- Cell Biology
Background:
- Platelet-activating factor (PAF) is a potent lipid mediator involved in inflammatory and immune responses.
- Understanding the molecular composition of PAF is crucial for elucidating its diverse biological functions.
Purpose of the Study:
- To investigate the molecular heterogeneity of PAF synthesized by different mammalian cell types.
- To determine if PAF biosynthesis exhibits species-specific or cell-specific precursor utilization.
Main Methods:
- Analysis of PAF molecular species using gas chromatography-negative ion chemical ionization mass spectrometry (GC-NICI-MS).
- Comparison of PAF composition in unstimulated and ionophore-stimulated polymorphonuclear leukocytes (PMN) from rats, mice, guinea pigs, and rat basophilic leukemia (RBL) cells.
Main Results:
- Multiple PAF molecular species (C14:0 to C19:0) were detected in all cell types studied.
- Each cell type displayed a unique PAF molecular species distribution, with distinct major and minor components.
- Rat PMN and RBL cells predominantly produced C16:0 PAF, while mouse PMN showed a mix including C18:1 and C18:0.
- Guinea pig PMN exhibited a more diverse profile, with significant C16:0 and C17:0 species.
Conclusions:
- PAF biosynthesis is characterized by significant molecular heterogeneity that is species-specific.
- Cells demonstrate a high degree of selectivity in utilizing precursor substrates for PAF synthesis.
- Stimulation with Ca2+ ionophore caused minor but significant alterations in PAF molecular species distribution.