The role of adenosine A 2 receptors in the regulation of TNF‐α production and PGE 2 release in mouse peritoneal macrophages

Abstract

The adenosine A2 receptors mediate most of the anti-inflammatory activities of adenosine. In LPS-stimulated macrophages adenosine inhibits TNF-α release, but may also enhance PGE2 generation. The aim of this study was to determine the relative contributions of the A2A and A2B receptors in these two effects and to determine whether the enhanced release of PGE2 contributed to the inhibition of TNF-α release. In LPS-stimulated mouse peritoneal macrophages, we confirmed that adenosine potently inhibited TNF-α production, but also potentiated PGE2 production. However, the potency of inhibition of TNF-α release was at least one order of magnitude higher than that for the potentiation of PGE2 generation (IC50= 250nM vs EC50=3μM). The non-selective adenosine receptor agonist NECA, and the selective A2A receptor agonist CGS 21680 also inhibited TNF-α production even more potently (IC50 = 5.7 and 2.4nM, respectively). NECA, but not CGS 21680, also enhanced PGE2 production. The selective A2A antagonist ZM 241385 (100nM), but not the selective A2B receptor antagonist MRS 1754 (100nM), blocked the inhibitory effect of NECA and CGS 21680 on TNF-α release. On the other hand, only MRS 1754 abolished the PGE2-potentiating effect of NECA. Pretreatment with indomethacin (1μM) abolished adenosine-induced PGE2 release but did not prevent the inhibition of TNF-α release. These results show that in this system, the inhibition of TNF-α release by adenosine is mediated by the A2A receptors whereas the enhancement of PGE2 release appears to be mediated by the A2B receptors. The results also show that the enhanced PGE2 release induced by adenosine does not appear to contribute to its ability to inhibit TNF-α release. This work was supported by grant No MR 01/04 from Research Administration, Kuwait University.