Abstract 3869: Adenosine Down-Regulates Toll-like Receptor -4 Activation
Background: Although cardioprotective properties of adenosine have been extensively studied, not much is known about its potential to limit the development of heart failure. Recent evidence suggests that activation of Toll-Like Receptor (TLR)-4 mediates adverse left ventricular (LV) remodeling. We hypothesized that adenosine may interfere with TLR4 activation.
Methods: Primary blood monocytes obtained from healthy volunteers and patients with acute myocardial infarction (MI) were differentiated to macrophages. Macrophages derived from the pro-monocytic cell line THP-1 were also used in this study. Cells were pre-treated with adenosine (10 μM), CGS21680 (A2a receptor agonist) or SCH58261 (A2a antagonist), before TLR4 activation by LPS (100 ng/mL), hyaluronic acid (HA, 50 μg/mL), or heparan sulphate (HS, 50μg/mL). Biochemical analyses included quantitative PCR, flow cytometry, ELISA, co-immunoprecipitation, immunoblotting, and protein cross-linking.
Results: Having observed that TLR4 expression is induced in MI patients (2-fold, P=0.0005), we showed that adenosine down-regulated TLR4 expression at the surface of human macrophages by 40% (P<0.05). Adenosine inhibited the phosphorylation of IκBα and p38, which suppressed the activation of IκBα/NF-κB and p38/AP-1 pathways. Adenosine down-regulated Tumor Necrosis Factor (TNF)- α production induced by the TLR4 ligands LPS, HA and HS by at least 75% (P<0.05). The A2a receptor agonist inhibited TNF-α production and the A2a antagonist had the opposite effect. Adenosine stimulated the binding of β-arrestins to TNF receptor-associated factor -6 (TRAF-6), a downstream effector of TLR4 activation. The effect of adenosine was replicated in macrophages isolated from patients with acute MI.
Conclusion: This study shows for the first time that adenosine down-regulates inflammation through interference with TLR4 activation. The effect is mediated through TLR4 internalization and enhanced binding of β-arrestins to TRAF-6. Our data strengthen the assumption that adenosine could be used to prevent LV remodeling.