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 A 2 receptors are known to mediate most of the anti-inflammatory activities of adenosine. In lipopolysaccharides (LPS)-stimulated macrophages adenosine strongly inhibits TNF-α release, but may also enhance PGE 2 generation. The aims of this study were to determine the relative contributions of the A 2A and A 2B receptor subclasses in these two effects and to determine whether the enhanced release of PGE 2 contributes to the inhibition of TNF-α release. In LPS-stimulated mouse macrophages, adenosine potently inhibited TNF-α production and also potentiated PGE 2 release, though less potently (IC 50 = 250 nM vs EC 50 ≈ 8 μM, respectively). The non-selective adenosine receptor agonist NECA, and the selective A 2A receptor agonist CGS21680 also inhibited TNF-α production even more potently (IC 50 = 4.8 and 2.3 nM, respectively). NECA, but not CGS21680, also enhanced PGE 2 production. The selective A 2A receptor antagonist ZM241385 (30 nM), but not the selective A 2B receptor antagonist MRS1754 (30 nM), blocked the inhibitory effect of NECA and CGS21680 on TNF-α release. On the other hand, MRS1754, but not ZM241385, abolished the PGE 2 potentiating effect of NECA. Pre-treatment with indomethacin (1 μM) abolished adenosine-induced PGE 2 release enhancement 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 A 2A receptors whereas the enhancement of PGE 2 release appears to be mediated by the A 2B receptors. The results also show that while exogenous PGE 2 is a potent inhibitor of TNF-α release, the enhanced PGE 2 release induced by adenosine does not appear to contribute to the inhibition of TNF-α release.