Inhibition by reproterol of cAMP PDE in intact mastocytoma P-815 cells

Abstract

In vitro studies in rat mastocytes and human monocytes suggested that reproterol (a selective β 2-adrenoceptor agonist with a theophylline moiety) exerts anti-inflammatory actions through inhibition of cyclic AMP (cAMP) PDE activity. Thus, reproterol was tested for its ability to inhibit cAMP PDE in cultured mouse mastocytoma P-815 cells. cAMP PDE activity was measured in intact cells by spectrofluorometry using the fluorescent substrate 2′- O-anthraniloyl cAMP. Reproterol was more potent than theophylline to inhibit cAMP PDE (pIC 50=4.28±0.25 vs. 3.16±0.05). This contrasted with disrupted cells, where the PDE inhibitory potency of reproterol was low (pIC 50=2.85±0.03) and similar to that of theophylline (pIC 50=2.66±0.19). No cAMP PDE inhibition was found with other β 2-agonists tested (fenoterol, salbutamol, salmeterol and formoterol). Finally, the selective PDE inhibitors calmidazolium (100 nM), milrinone (5 μM) and rolipram (50 μM) inhibited cAMP PDE activity by ≈20, 30 and 25% respectively. In conclusion, reproterol potently and non-specifically inhibited intracellular cAMP phosphodiesterases in intact mastocytoma cells. This can explain the previously reported β 2-adrenoceptor-independent anti-inflammatory actions of reproterol in vitro. Further studies are required to define the anti-inflammatory potential of reproterol in asthma.