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Amplification of LTB4 generation in AM-PMN cocultures: transcellular 5-lipoxygenase metabolism
F Grimminger1, U Sibelius, W Seeger
1Department of Internal Medicine, Justus-Liebig-University Giessen, Federal Republic of Germany.
Abstract:
The generation of arachidonic acid (AA) metabolites by human polymorphonuclear leukocytes (PMN) and by rabbit alveolar macrophages (AM) was investigated and compared with that produced under conditions of coculture. Incubation of PMN with the calcium ionophore A23187 resulted in rapid generation of leukotriene (LT) B4 and its omega-oxidation products, paralleled by substantial secretion of 5-hydroxyeicosatetraenoic acid (HETE) and intact LTA4. Rapid LTA4 decay to nonenzymatic hydrolysis products in the extracellular space ensued. Exogenous AA, offered simultaneously with the ionophore, markedly increased 5-lipoxygenase product formation. Incubation of AM with A23187 evoked protracted generation of LTB4 in the absence of omega-oxidation, with concomitant liberation of 5-HETE, 15-HETE, free AA, and minor amounts of AA cyclooxygenase products. Exogenously offered LTA4 was avidly taken up and converted into LTB4 by these cells. Costimulation of AM and PMN with the ionophore resulted in an approximately 2.5-fold increase in the generation of LTB4 and its metabolites (compared with the summed amounts of the isolated cell experiments), whereas 5-HETE and nonenzymatic LTA4, hydrolysis product formation were markedly reduced. This change in metabolite profile was dependent on the AM-to-PMN ratio. Acetylsalicylic acid increased 5-lipoxygenase product formation in the coculture studies but not in the isolated cell experiments. AA prelabeling of either PMN or AM resulted in radioactivity detection in all AA lipoxygenase products except for 15-HETE.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Human polymorphonuclear leukocytes (PMN) and alveolar macrophages (AM) generate arachidonic acid (AA) metabolites differently. Coculture enhances leukotriene B4 (LTB4) production, suggesting synergistic interactions between these immune cells.
Area of Science:
- Biochemistry
- Immunology
- Cell Biology
Background:
- Human polymorphonuclear leukocytes (PMN) and rabbit alveolar macrophages (AM) produce distinct arachidonic acid (AA) metabolites.
- Understanding these differences is crucial for investigating inflammatory pathways and immune cell interactions.
Purpose of the Study:
- To investigate and compare the generation of AA metabolites by isolated human PMN and rabbit AM.
- To examine the metabolic profile of these cells during coculture conditions.
Main Methods:
- Incubation of isolated PMN and AM with the calcium ionophore A23187.
- Analysis of leukotriene (LT) B4, 5-hydroxyeicosatetraenoic acid (HETE), and other AA metabolite production.
- Coculture experiments with varying AM-to-PMN ratios and assessment of metabolite generation.
Main Results:
- PMN rapidly generated LTB4 and its omega-oxidation products, while AM produced LTB4 with less omega-oxidation and released more free AA and 15-HETE.
- Coculture of PMN and AM significantly increased LTB4 generation (approx. 2.5-fold) compared to isolated cells, with reduced 5-HETE and LTA4 hydrolysis.
- The observed changes in metabolite profiles during coculture were dependent on the AM-to-PMN ratio and influenced by acetylsalicylic acid.
Conclusions:
- Human PMN and rabbit AM exhibit distinct AA metabolic capabilities.
- Coculture enhances LTB4 production, indicating synergistic interactions between PMN and AM.
- The AM-to-PMN ratio critically influences the metabolite profile in coculture systems.