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Prostaglandin E2 mediates lipopolysaccharide-induced macrophage procoagulant activity by a cyclic adenosine
J G Williams1, I Garcia, R V Maier
1Department of Surgery, University of Texas Southwestern Medical Center, Dallas 75235-9031.
Background:
Multiple organ failure syndrome (MOFS) and adult respiratory distress syndrome (ARDS) continue to be significant clinical problems. Microvascular thrombosis and intraalveolar fibrin deposition play an integral role in the pathogenesis of MOFS and ARDS. The macrophage participates in these processes by expressing procoagulant activity (PCA) after exposure to endotoxin. One potential method to ameliorate organ dysfunction in ARDS and MOFS is to prevent macrophage activation of the coagulation cascade. Because inhibitors of arachidonic acid metabolism attenuate inflammatory lung injury, we investigated the role of eicosanoids in endotoxin-induced alveolar macrophage PCA.
Methods:
Rabbit alveolar macrophages were incubated with selective inhibitors of arachidonic acid metabolism. PCA was determined in cell lysates. PCA was also assessed in cultures treated with cyclooxygenase inhibitor that had exogenous prostaglandin E2 (PGE2) added. Intracellular cyclic adenosine monophosphate (cAMP) was examined after treatment with lipopolysaccharide, ibuprofen, PGE2, and forskolin.
Results:
Ibuprofen significantly reduces lipopolysaccharide-stimulated PCA by alveolar macrophages. 5-Lipoxygenase and thromboxane synthetase inhibitors had no effect on PCA. Inhibition of PCA by ibuprofen is reversed by adding exogenous PGE2. Decreased intracellular cAMP is associated with attenuated lipopolysaccharide-stimulated PCA elaboration.
Conclusions:
Endotoxin-stimulated alveolar macrophage PCA is prostanoid dependent, with cAMP acting as a second messenger. Although expression of PCA is prostanoid-cAMP dependent, neither prostanoids nor agents that directly increase cAMP are sufficient to elicit PCA in the absence of lipopolysaccharide.
Insights
Endotoxin stimulates macrophages to promote blood clotting, contributing to organ failure. Inhibiting prostaglandin production with ibuprofen reduces this clotting activity, suggesting a therapeutic target for ARDS and MOFS.
Area of Science:
- Pulmonary Medicine
- Immunology
- Coagulation Science
Background:
- Adult respiratory distress syndrome (ARDS) and multiple organ failure syndrome (MOFS) are critical clinical issues.
- Microvascular thrombosis and intraalveolar fibrin deposition are key in ARDS and MOFS pathogenesis.
- Macrophages, upon endotoxin exposure, exhibit procoagulant activity (PCA), contributing to these pathological processes.
Purpose of the Study:
- To investigate the role of eicosanoids in endotoxin-induced alveolar macrophage PCA.
- To explore potential therapeutic strategies for organ dysfunction in ARDS and MOFS by preventing macrophage activation of the coagulation cascade.
Main Methods:
- Rabbit alveolar macrophages were treated with selective inhibitors of arachidonic acid metabolism.
- Procoagulant activity (PCA) was measured in cell lysates and cultures.
- Intracellular cyclic adenosine monophosphate (cAMP) levels were assessed following treatment with lipopolysaccharide, ibuprofen, prostaglandin E2 (PGE2), and forskolin.
Main Results:
- Ibuprofen significantly inhibited lipopolysaccharide-stimulated PCA in alveolar macrophages.
- Inhibitors of 5-lipoxygenase and thromboxane synthetase did not affect PCA.
- The inhibitory effect of ibuprofen on PCA was reversed by the addition of exogenous PGE2.
- Decreased intracellular cAMP levels correlated with reduced lipopolysaccharide-stimulated PCA.
Conclusions:
- Endotoxin-induced alveolar macrophage PCA is dependent on prostanoids, with cAMP acting as a crucial second messenger.
- While prostanoids and cAMP are essential for PCA expression, they are insufficient to induce PCA without endotoxin stimulation.