Anti-inflammatory effects of exogenous uridine in an animal model of lung inflammation

Nucleosides like adenosine, uridine and their nucleotide derivatives (e.g. ATP and UTP) play important roles in many cellular functions, sometimes by acting as signalling molecules through binding to specific P2 nucleotide receptors. P2 receptors are subdivided into P2X and P2Y subfamilies, the latter of which are G-protein coupled receptors. P2Y receptors and nucleoside transporters have been detected in human and rat lungs, where they mediate effects of interest in airway diseases. The aim of this study was to investigate whether uridine has any anti-inflammatory properties in an asthma-like animal model of lung inflammation. The Sephadex-induced lung inflammation model in Sprague-Dawley rats was chosen mainly due to its localised inflammatory response and uridine's limited oral bioavailability. The dextran beads, with or without the addition of uridine, were instilled intratracheally into the lungs, which were excised and examined after 24 h. Sephadex alone led to massive oedema and infiltration of macrophages, neutrophils and eosinophils. Microgranulomas with giant cell formations were clearly visible around the partially degraded beads. Uridine reduced both the oedema and the infiltration of leukocytes significantly, measured as lung wet weight and leukocyte counts in bronchoalveolar lavage fluid, respectively. Uridine appeared to affect the tumour necrosis factor (TNF) levels, although this could not be statistically confirmed due to large variations within the Sephadex control group. We conclude that uridine has anti-inflammatory effects, and that the exact mechanism(s) of action requires further study.