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Cyclic-AMP level and eicosanoid release from alveolar macrophages are differentially affected by high and low dose of
F D Beusenberg1, I L Bonta, J G van Amsterdam
1Department of Pharmacology, Erasmus University Rotterdam, The Netherlands.
Abstract:
Antigen challenged alveolar macrophages (ac-AM) showed much higher basal prostaglandin E2 (PGE2) release (4,4-fold) and cAMP content (2,4-fold) than naive alveolar macrophages (AM). In naive AM 1 fM platelet activating factor (PAF) enhanced PGE2 release from 115 to 157 ng/5 x 10(6) cells but was inactive at 1 nM or 1 microM. In ac-AC 1 fM PAF enhanced PGE2 release from 510 to 670 ng/5 x 10(6) cells and inhibited leukotriene B4 (LTB4) release (from 6.0 to 4.8 ng/5 x 10(6) cells). At a 10(6)-fold higher concentration PAF inhibited PGE2 release (from 510 to 400 ng/5 x 10(6) cells) and stimulated LTB4 release (from 6.0 to 8.2 ng/5 x 10(6) cells). PAF-induced increase or decrease in PGE2 release was paralleled by changes in cellular cAMP (+35 and -17%, respectively). The specific PAF-antagonist BN 52021 completely reversed all PAF-induced effects while indomethacin inhibited only PAF-induced increase in PGE2 release and cAMP leaving LTB4 release unaffected. Similarly, the lipoxygenase inhibitor AA-861 inhibited PAF-induced rise in LTB4 release leaving the enhancement in PGE2 release and cAMP content unaffected. Present data show that PAF dose-dependently affects eicosanoid production and cAMP level in alveolar macrophages.
Insights
Platelet-activating factor (PAF) dose-dependently alters prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) release in alveolar macrophages. These effects are linked to changes in cellular cyclic adenosine monophosphate (cAMP) levels.
Area of Science:
- Immunology
- Cell Biology
- Pharmacology
Background:
- Alveolar macrophages (AM) play a crucial role in lung immunity.
- Prostaglandin E2 (PGE2) and Leukotriene B4 (LTB4) are key inflammatory mediators.
- Platelet-activating factor (PAF) is implicated in inflammatory responses.
Purpose of the Study:
- To investigate the dose-dependent effects of PAF on eicosanoid production and cAMP levels in naive and antigen-challenged AM.
- To elucidate the signaling pathways involved in PAF-mediated effects on AM.
Main Methods:
- Primary alveolar macrophages were isolated from naive and antigen-challenged rabbits.
- Cells were stimulated with varying concentrations of PAF.
- PGE2 and LTB4 release were measured using enzyme immunoassays.
- Intracellular cAMP levels were quantified.
- Specific PAF antagonists and enzyme inhibitors were used to probe signaling pathways.
Main Results:
- Antigen-challenged AM exhibited higher basal PGE2 release and cAMP content compared to naive AM.
- Low-dose PAF (1 fM) enhanced PGE2 release and inhibited LTB4 release in antigen-challenged AM, accompanied by increased cAMP.
- High-dose PAF (1 microM) inhibited PGE2 release and stimulated LTB4 release in antigen-challenged AM, with decreased cAMP.
- PAF-induced effects were reversed by a specific PAF antagonist.
- Indomethacin (COX inhibitor) blocked PAF-induced PGE2 increase but not LTB4 changes.
- AA-861 (lipoxygenase inhibitor) blocked PAF-induced LTB4 increase but not PGE2 changes.
Conclusions:
- PAF exerts dose-dependent and differential effects on PGE2 and LTB4 production in alveolar macrophages.
- These effects are mediated through distinct signaling pathways involving cyclic AMP.
- The findings highlight the complex role of PAF in regulating inflammatory mediator release by AM.