Immunopharmacology and Inflammation Adenosine A 2A receptors and uric acid mediate protective effects of inosine against TNBS-induced colitis in rats Reza Rahimian a , Gohar Fakhfouri b , Ali Daneshmand c , Hamed Mohammadi a , Arash Bahremand a , Mohammad Reza Rasouli a , Kazem Mousavizadeh d , Ahmad Reza Dehpour a, ⁎ a Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran b Department of Pharmacology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran c Interdisciplinary Neuroscience Research Program (INRP), Tehran University of Medical Sciences, Tehran, Iran d Department of Basic Sciences and Cellular and Molecular Research Center and Oncopathology research center, Iran University of Medical Sciences, Tehran, Iran abstract article info Article history: Received 29 May 2010 Received in revised form 28 August 2010 Accepted 7 September 2010 Available online 22 September 2010 Keywords: Inosine Uric acid Adenosine receptor Inflammatory bowel disease Inflammatory bowel disease comprises chronic recurrent inflammation of gastrointestinal tract. This study was conducted to investigate inosine, a potent immunomodulator, in 2,4,6-trinitrobenzene sulphonic acid (TNBS)-induced chronic model of experimental colitis, and contribution of adenosine A 2A receptors and the metabolite uric acid as possible underlying mechanisms. Experimental colitis was rendered in rats by a single colonic administration of 10 mg of TNBS. Inosine, potassium oxonate (a hepatic uricase inhibitor), SCH- 442416 (a selective adenosine A 2A receptor antagonist), inosine + potassium oxonate, or inosine + SCH- 442416 were given twice daily for 7 successive days. At the end of experiment, macroscopic and histopathologic scores, colonic malondialdehyde (MDA), Tumor Necrosis Factor-alpha (TNF-α) and Interleukin-1beta (IL-1β) levels, and myeloperoxidase (MPO) activity were assessed. Plasma uric acid level was measured throughout the experiment. Both macroscopic and histological features of colonic injury were markedly ameliorated by either inosine, oxonate or inosine + oxonate. Likewise, the elevated amounts of MPO and MDA abated as well as those of TNF-α and IL-1β (P b 0.05). SCH-442416 partially reversed the effect of inosine on theses markers, while inosine + oxonate showed a higher degree of protection than each treatment alone (P b .0.05). No significant difference was observed between TNBS and SCH-442416 groups. Uric acid levels were significantly higher in inosine or oxonate groups compared to control. Inosine + oxonate resulted in an even more elvelated uric acid level than each treatment alone (P b 0.05). Inosine elicits notable anti-inflammatory effects on TNBS-induced colitis in rats. Uric acid and adenosine A 2A receptors contribute to these salutary properties. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Ulcerative colitis and Crohn's disease, collectively termed inflam- matory bowel disease, have received enormous attention in recent years. Inflammatory bowel disease is characterized by recurrent inflammation and disruption of gut wall resulting from leukocyte infiltration and excessive generation of inflammatory mediators and oxidants. The aetiology is still unclear and presumed to encompass genetic, environmental and immunologic factors (Podolsky, 2002). Reactive oxygen species such as hydrogen peroxide, superoxide anion or hydroxyl radicals, and specially, reactive nitrogen species such as peroxynitrite, are implicated in pathogenesis of inflammatory bowel disease (Fillmann et al., 2007; Pavlick et al., 2002; Yoshida et al., 1999). The pro-inflammatory roles of these reactive species include recruitment of more neutrophils at the site of inflammation, formation of chemotactic factors, lipid peroxidation, and release of cytokines, such as Interleukine-1beta (IL-1β) and Tumor Necrosis Factor-alpha (TNF-α)(Mazzon et al., 2006). Interestingly, mucosal antioxidant components, such as glutathione, urate and alpha- tocopherol are depleted in human inflammatory bowel disease. Such deficit in antioxidant defence leaves the space for oxidizing agents to inflict damage on the compromised mucosa and hampers recovery of its intact architecture (Buffinton and Doe, 1995). At present, the management of inflammatory bowel disease is based on two classes of drugs; aminosalicylates and corticosteroids. These agents reduce inflammation and ameliorate the expression of pro- inflammatory mediators but their untoward effects have constrained their long-term use (Baumgart and Sandborn, 2007). It is therefore necessary to investigate new agents as an alternative therapy in inflammatory bowel disease. Inosine has been used traditionally as an energy supplement and performance enhancer (Starling et al., 1996). Ample evidence has European Journal of Pharmacology 649 (2010) 376–381 ⁎ Corresponding author. Tel.: + 98 21 8897 3652; fax: + 98 21 66402569. E-mail address: dehpour@yahoo.com (A.R. Dehpour). 0014-2999/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ejphar.2010.09.044 Contents lists available at ScienceDirect European Journal of Pharmacology journal homepage: www.elsevier.com/locate/ejphar