Suppression of macrophage inflammatory protein (MIP)-1α production and collagen-induced arthritis by adenosine receptor agonists

Abstract

1. Ligands of the various adenosine receptor subtypes modulate the production of pro-and anti-inflammatory cytokines. Here we evaluated the effect of adenosine and various ligands of the adenosine receptor subtypes (A₁, A₂, A₃) on the chemokine macrophage inflammatory protein (MIP) 1α production in immunostimulated RAW macrophages in vitro. Furthermore, we studied whether a selected A₃ adenosine receptor agonist inhibits MIP-1α production and affects the course of inflammation in collagen-induced arthritis.

2. In the cultured macrophages, 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-ethyl-carboxamidoadenosine (CGS; 1–200 μM) dose-dependently suppressed the production of MIP-1α. The selective A₁ receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA, 1–200 μM) was ineffective, and adenosine was a weak inhibitor. The inhibition of MIP-1α production by the A₃ and A₂ agonist was associated with suppression of its steady-state mRNA levels.

3. Based on the in vitro data, we concluded that activation of A₃, and to a lesser extent A₂ adenosine receptors suppresses MIP-1α expression. Since IB-MECA was the most potent inhibitor of MIP-1α expression, we next investigated whether it affects the production of other pro-inflammatory mediators. We observed that IB-MECA (1–300 μM) inhibited, in a dose-dependent manner, the production of IL-12, IL-6, and, to a lesser extent, nitric oxide in the immunostimulated cultured macrophages.

4. Since MIP-α is a chemokine which enhances neutrophil recruitment into inflammatory sites, we investigated whether the A₃ agonist IB-MECA affects the course of inflammation, MIP-α production and the degree of neutrophil recruitment in arthritis. In a model of collagen-induced arthritis in mice, IB-MECA (0.5 mg/kg/day) reduced the severity of joint inflammation. IB-MECA inhibited the formation of MIP-1α, IL-12 and nitrotyrosine (an indicator of reactive nitrogen species) in the paws, and suppressed neutrophil infiltration.

5. We conclude that adenosine receptor agonists, most notably the A₃ agonist IB-MECA suppress the production of MIP-α, and exert anti-inflammatory effects. Therefore, stimulation of adenosine receptor subtypes A₃ and A₂ may be a strategy worthy of further evaluation for the abrogation of acute or chronic inflammatory disorders.

Full Text

The Full Text of this article is available as a PDF (949.9 KB).