Adenosine receptor agonists suppress macrophage inflammatory protein -1α production and collagen induced arthritis

Abstract

The production of pro- and anti-inflammatory cytokines is modulated by ligands of various adenosine receptor subtypes. In this study, we looked at how adenosine and different ligands for the adenosine receptor subtypes (A1, A2, A3) affected the production of the chemokine macrophage inflammatory protein (MIP) 1a in immune-stimulated RAW macrophages in vitro. In addition, we investigated whether an A3 adenosine receptor agonist reduces MIP-1α production and influences the course of inflammation in collagen-induced arthritis. The A3 receptor agonist N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (IB-MECA) and, less potently, the A2 receptor agonist 2-p-(2-carboxyethyl) phenethylamino-5'-N-ethylamino-5'-N-ethylamino-5'-N- ethylamino-5'-N Adenosine was a mild inhibitor, and the selective A1 receptor agonist 2-chloro- N-cyclopentyladenosine (CCPA, 1 200 M) proved ineffective. MIP-1α production is inhibited by suppression of its steady-state mRNA levels and was linked to the A3 and A2 agonists. We concluded that stimulation of A3 and, to a lesser extent, A2 adenosine receptors decreases MIP-1α expression based on our in vitro findings. We studied whether IB-MECA, as the most powerful inhibitor of MIP-1α expression, also influences the production of other pro-inflammatory mediators. IB- MECA (1 300 M) reduced the production of IL-12, IL-, and, to a lesser extent, nitric oxide in immune-stimulated cultured macrophages in a dose-dependent manner. We explored whether the A3 agonist IB-MECA alters the course of inflammation, MIP-a production, and the degree of neutrophil recruitment in arthritis because MIP-α is a chemokine that increases neutrophil recruitment into inflammatory areas. In the case of IB- MECA (0.5 mg/kg/day) decreased the degree of joint inflammation in a mouse model of collagen-induced arthritis. IB-MECA decreased neutrophil infiltration and inhibited the production of MIP-1α, IL-12, and nitrotyrosine (a marker of reactive nitrogen species) in the paws. We conclude that adenosine receptor agonists, particularly the A3 agonist IB-MECA, inhibit MIP-α synthesis and have anti-inflammatory properties. As a result, stimulating adenosine receptor subtypes A3 and A2 may be a promising technique for the treatment of acute and chronic inflammatory diseases.