The Blockade of Adenosine Deaminase Ameliorates Chronic Experimental Colitis through the Recruitment of Adenosine A_2Aand A₃Receptors

Abstract

Adenosine modulates immune/inflammatory reactions. This study investigates the expression of adenosine deaminase in the inflamed colon, the effects of adenosine deaminase inhibitors on established colitis, and the recruitment of adenosine receptors by endogenous adenosine after adenosine deaminase blockade. Adenosine deaminase expression was determined by Western blot. The effects of 4-amino-2-(2-hydroxy-1-decyl)pyrazole [3,4-d]pyrimidine (APP; a novel adenosine deaminase inhibitor), erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA; a reference adenosine deaminase inhibitor), dexamethasone, and selective adenosine receptor antagonists were tested in rats with 2,4-dinitrobenzenesulfonic acid-induced colitis. Systemic (food intake, body and spleen weight) and colonic [macroscopic/microscopic damage, tumor necrosis factor-␣ (TNF-␣), interleukin-6 (IL-6), and malondialdehyde (MDA)] inflammatory parameters were assessed. Test drugs were administered intraperitoneally for 6 days, starting at day 5 from colitis induction. Adenosine deaminase was detected in normal colon, and its expression was increased in inflamed tissues. Colitis was associated with decreased food intake and body weight, augmented spleen weight, and increased levels of colonic TNF-␣, IL-6, and MDA. APP or EHNA, but not dexamethasone, improved food intake and body weight. APP, EHNA, and dexamethasone counteracted the increments of spleen weight, ameliorated macroscopic and microscopic indexes of inflammation, and reduced TNF-␣, IL-6, and MDA levels. The beneficial effects of APP and EHNA on inflammatory parameters were prevented by the pharmacological blockade of A 2A or A 3 receptors, but not A 1 or A 2B . The present results show that: 1) bowel inflammation is associated with an enhanced adenosine deaminase expression; and 2) the anti-inflammatory actions of adenosine deaminase inhibitors against chronic established colitis depend on the sparing of endogenous adenosine, leading to enhanced A 2A and A 3 receptor activation.

Gs-Coupled Adenosine Receptors Differentially Limit Antigen-Induced Mast Cell Activation

“…It is possible that the environment in which the mast cell resides influences adenosine receptor expression and function, accounting for the differences in receptor effects observed between these studies. Although several studies have suggested that A 2A receptors mediate anti-inflammatory effects (Antonioli et al, 2010;Fenster et al, 2000;Harada et al, 2000;Kreckler et al, 2006;Rork et al, 2008;Trevethick et al, 2008), a clinical trial failed to demonstrate efficacy of an A 2A agonist in attenuating allergen-induced early and late reactions, sputum total cell counts and EG21 cell numbers, eosinophil cationic protein levels, or inflammatory cytokine production in asthmatic subjects (Luijk et al, 2008).…”

Adenosine A2A Receptors: Localization and Function

“…However, the best-characterized effect of A 2A receptors at this level is related to the modulation of intestinal inflammation, and a marked up-regulation of highaffinity A 2A receptors has been observed in experimental colitis (Antonioli et al 2006(Antonioli et al , 2008. Importantly, independent studies have shown that the stimulation of A 2A receptors attenuates inflammatory responses in the colon (Antonioli et al 2010;Odashima et al 2005;Rahimian et al 2010), although it has to be acknowledged that others failed to observe this effect (Selmeczy et al 2007). Adenosine A 2A receptors have also been shown to modulate inflammation and tissue damage in the lung, as demonstrated by several preclinical studies (Eckle et al 2009;Trevethick et al 2008;Wilson et al 2009).…”

Anti-inflammatory effect of a novel locally acting A2A receptor agonist in a rat model of oxazolone-induced colitis

“…TNF levels in colonic tissues were measured by an ELISA kit (Abcam), as previously described [1]. For this purpose, colonic tissue samples, stored previously at − 80°C, were weighed, thawed, and homogenized in 0.4 ml of pH 7.2 PBS/20 mg of tissue at 4°C and centrifuged at 10,000×g for 5 min.…”

“…Inflammatory bowel diseases (IBDs) are chronic, idiopathic inflammatory disorders characterized by alternating periods of active disease or flare-ups and remission, with highly negative impact on well-being and patient's quality of life [1]. Although the precise etiological factors leading to the onset of these chronic inflammatory conditions remain unclear, increasing evidence supports the concept that IBDs arise from altered and complex interactions of environmental, genetic, and immunological factors [2].…”