Effect of Novel A2AAdenosine Receptor Agonist ATL 313 onClostridium difficileToxin A-Induced Murine Ileal Enteritis

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Abstract
Clostridium difficileis a spore-forming, anaerobic, gram-positive bacillus that releases two main virulence factors: toxins A and B. Toxin A plays an important pathogenic role in antibiotic-induced diarrhea and pseudomembranous colitis, a condition characterized by intense mucosal inflammation and secretion. Agonist activity at A2Aadenosine receptors attenuates inflammation and damage in many tissues. This study evaluated the effects of a new selective A2Aadenosine receptor agonist (ATL 313) on toxin A-induced injury in murine ileal loops. ATL 313 (0.5 to 5 nM) and/or the A2Aadenosine receptor antagonist (ZM241385; 5 nM) or phosphate-buffered saline (PBS) were injected into ileal loops immediately prior to challenge with toxin A (1 to 10 μg/loop) or PBS. Intestinal fluid volume/length and weight/length ratios were calculated 3 h later. Ileal tissues were collected for the measurement of myeloperoxidase, adenosine deaminase activity, tumor necrosis factor alpha (TNF-α) production, histopathology, and detection of cell death by the TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) method. Toxin A significantly increased volume/length and weight/length ratios in a dose-dependent fashion. ATL 313 treatment significantly (P< 0.05) reduced toxin A-induced secretion and edema, prevented mucosal disruption, and neutrophil infiltration as measured by myeloperoxidase activity. ATL 313 also reduced the toxin A-induced TNF-α production and adenosine deaminase activity and prevented toxin A-induced cell death. These protective effects of ATL 313 were reversed by ZM241385. In conclusion, the A2Aadenosine receptor agonist, ATL 313, reduces tissue injury and inflammation in mice with toxin A-induced enteritis. The finding of increased ileal adenosine deaminase activity following the administration of toxin A is new and might contribute to the pathogenesis of the toxin A-induced enteritis by deaminating endogenous adenosine.