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Arachidonate metabolism triggered in primed macrophages by signals inducing antitumor activity
K Raddassi1, J P Tenu, P Pradelles
1URA CNRS 1116, Université Paris-Sud, Orsay, France.
Abstract:
The acquisition of antitumoral functions by mouse peritoneal macrophages is controlled by the addition of activating agents (lipopolysaccharide (LPS), muramyldipeptide (MDP) or A23187), on appropriately primed macrophages. The release of eicosanoids during this activation step was examined by radio-HPLC. We demonstrated that the induction of antitumor activity in primed macrophages by LPS or MDP was associated with the release of 20:4 derivatives; arachidonic acid was metabolized predominantly via the cyclooxygenase pathway to PGE2 and thromboxane. The production of PGE2, quantified by an enzyme immunoassay, was sustained and important (up to 20 ng/ml/h/10(6) macrophages). However, PGE2 and thromboxane did not seem essential to the activation process: induction of antitumor activity took place and was even enhanced in the presence of indomethacin, whereas it was decreased by exogenous PGE2. During culture in vitro, primed macrophages released spontaneously significant amounts of 20:4 metabolites and became unresponsive to activation stimuli. Again indomethacin had a positive effect: it protected primed macrophages against this loss of activability. Cyclooxygenase metabolites released in response to activating stimuli or spontaneously seem to trigger deactivation pathways.
Insights
Activating mouse macrophages with agents like LPS enhances their tumor-fighting ability, involving arachidonic acid metabolism. However, cyclooxygenase products like PGE2 are not essential and may even hinder this antitumor activity.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Mouse peritoneal macrophages can acquire antitumoral functions when activated by specific agents.
- Eicosanoid release is a known response of activated macrophages.
Purpose of the Study:
- To investigate the role of eicosanoids, particularly cyclooxygenase metabolites, in the acquisition of antitumoral functions by primed mouse macrophages.
- To determine if these metabolites are essential for or modulate macrophage activation and antitumor activity.
Main Methods:
- Primed mouse peritoneal macrophages were activated with lipopolysaccharide (LPS), muramyldipeptide (MDP), or A23187.
- Eicosanoid release was analyzed using radio-high-performance liquid chromatography (radio-HPLC).
- Prostaglandin E2 (PGE2) production was quantified via enzyme immunoassay.
Main Results:
- Activation by LPS or MDP induced the release of 20:4 (arachidonic acid) derivatives, primarily via the cyclooxygenase pathway, producing PGE2 and thromboxane.
- PGE2 production was significant, but its inhibition with indomethacin enhanced, not decreased, antitumor activity.
- Exogenous PGE2 reduced antitumor activity, and indomethacin protected macrophages from spontaneous deactivation in vitro.
Conclusions:
- Cyclooxygenase metabolites, including PGE2 and thromboxane, are released during macrophage activation but are not essential for inducing antitumoral activity.
- These metabolites may play a role in deactivation pathways, as their inhibition enhances and their presence can impair antitumor functions.
- Indomethacin protects primed macrophages from losing activability during in vitro culture.