Adenosine A3 receptors on human eosinophils mediate inhibition of degranulation and superoxide anion release

摘要

class="enumerated" style="list-style-type:decimal">The role of adenosine A3 receptors on human eosinophil degranulation and superoxide anion (O2⁻) release was studied in vitro using the complement fragment C5a as the main stimulus and employing a number of selective agonists and antagonists.In the presence of cytochalasin B (CB), C5a induced a dose-dependent release of the granular eosinophil peroxidase (EPO), but not O2⁻, whereas in the absence of CB O2⁻, but not EPO, was released.C5a-induced EPO release was inhibited dose-dependently by the selective A3 agonist N⁶-(3-iodobenzyl)-5′-N-methylcarbamoyladenosine (IB-MECA) and to a lesser extent by the less-selective N⁶-2-(4-amino-3-iodophenyl) ethyladenosine (APNEA). The IC50 (95% CI) for IB-MECA was 6.8 μM (3.1–12.0 μM). At concentrations up to 100 μM, neither adenosine nor the selective A1 agonist N-cyclopentyladenosine (CPA) and the selective A2 agonist 2-[[2-[4-(2-carboxyethyl)phenyl]ethyl]amino]-N-ethylcarboxamidoadenosine (CGS 21680) had any significant effect.The inhibitory effect of IB-MECA was almost completely abolished by pre-treatment with 1 μM of the selective A3 antagonist 9-chloro-2-(2-furyl)-5-phenylactylamino[1,2,4]triazolo[1,5-c]quinazoline (MRS 1220), but not the selective A1 antagonist 1,3-dipropyly-8-cyclopentylxanthine (DPCPX) or the selective A2 antagonist 3,7-dimethyl-1-propargylxanthine (DMPX).IB-MECA also significantly inhibited C5a-induced O2⁻ release with IC50 (95% CI) of 9.5 μM (4.6–13.1 μM) whereas adenosine and the A1 agonist CPA potentiated this effect at low concentrations. The potentiation appeared to be a result of their direct O2⁻ release from these cells, probably mediated via A1 receptors. The inhibition by IB-MECA was selectively reversed by MRS 1220.These results show that the A₃ receptors on human eosinophils mediate inhibition of both degranulation and O₂⁻ release and suggest a therapeutic potential for A₃ agonists in diseases such as asthma in which activated eosinophils are involved.