title: Adenosine A3 receptors on human eosinophils mediate inhibition of degranulation and superoxide anion release.
abstract: 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 microM (3.1-12.0 microM). At concentrations up to 100 microM, 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 microM of the selective A3 antagonist 9-chloro-2-(2-furyl)-5-phenylactylamino[1,2,4]triazolo[1,5-c]quina zoline (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 microM (4.6-13.1 microM) 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.
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Medicine, Kuwait University, Safat. ezeamuzie@hsc.kuniv.edu.kw
authors.forename: C I
authors.initials: CI
authors.lastname: Ezeamuzie
authors.forename: E
authors.initials: E
authors.lastname: Philips
mesh_terms: D015550:Cell Degranulation / Q000187:drug effects / Q000502:physiology*; D015936:Complement C5a / Q000378:metabolism; D003571:Cytochalasin B / Q000494:pharmacology; D047209:Eosinophil Peroxidase; D004804:Eosinophils / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D010544:Peroxidases / Q000378:metabolism; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1 / Q000502:physiology*; D013481:Superoxides / Q000378:metabolism*
chemical_list: D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1; D013481:Superoxides; D003571:Cytochalasin B; D015936:Complement C5a; D047209:Eosinophil Peroxidase; D010544:Peroxidases