2-chloro-n(6)-(3-iodobenzyl)adenosine-5--n-methyluronamide and Inflammation

Adenosine possesses potent anti-inflammatory properties which are partly mediated by G(i) -coupled adenosine A3 receptors (A3Rs). A3R agonists have shown clinical benefit in a number of inflammatory conditions although some studies in A3R-deficient mice suggest a pro-inflammatory role. We hypothesised that, in addition to cell signalling effects, A3R compounds might inhibit neutrophil chemotaxis by disrupting the purinergic feedback loop controlling leukocyte migration. Human neutrophil activation triggered rapid upregulation of surface A3R expression which was disrupted by pre-treatment with either agonist (Cl-IB-MECA) or antagonist (MRS1220). Both compounds reduced migration velocity and neutrophil transmigration capacity without impacting the response to chemokines per se. Similar effects were observed in murine neutrophils, while cells from A3R-deficient mice displayed a constitutively impaired migratory phenotype indicating compound-induced desensitisation and genetic ablation had the same functional outcome. In a dextran sodium sulphate-induced colitis model, A3R-deficient mice exhibited reduced colon pathology and decreased tissue myeloperoxidase levels at day 8 - consistent with reduced neutrophil recruitment. However, A3R-deficient mice were unable to resolve the dextran sodium sulphate-induced inflammation and had elevated numbers of tissue-associated bacteria by day 21. Our data indicate that A3Rs play a role in neutrophil migration and disrupting this function has the potential to adversely affect innate immune responses.

Topics: Adenosine; Adenosine A3 Receptor Agonists; Adenosine A3 Receptor Antagonists; Animals; Chemotaxis; Colitis; Dextran Sulfate; Disease Models, Animal; Humans; Immunity, Innate; Inflammation; Mice; Mice, Knockout; Neutrophils; Quinazolines; Receptor, Adenosine A3; Triazoles; Up-Regulation

The activation of the adenosine A3 receptor (A3AR) can regulate inflammation, but the way that this regulates colonic mucosal inflammation in ulcerative colitis (UC) remains unclear. This study aimed at examining A3AR expression and investigating the effect of A3AR activation on ex vivo cytokine expression and nuclear factor-kappa B (NF-κB) signaling in colonic mucosa.. Colonic mucosal biopsied tissue from 18 patients with UC and 11 healthy controls was tested for A3AR expression by immunofluorescence, quantitative real-time polymerase chain reaction and Western blot. Following treatment for 24 hours with or without 2-Cl-IB-MECA, an A3AR agonist, TNF-α and IL-1β secreted by the cultured colonic mucosal tissue were quantified by ELISA. The colonic mucosal epithelia were dissected and treated with, or without 2-Cl-IB-MECA for 24 hours. The NF-κB p65 protein and its distribution in the cultured colonic epithelia were examined by immunofluorescence and Western blot.. Compared with the controls, down-regulated A3AR expression and up-regulated TNF-α and IL-1β production and NF-κB p65 protein were observed in the UC colonic mucosa. The activation of A3AR by 2-Cl-IB-MECA significantly decreased TNF-α and IL-1β production and attenuated the NF-κB p65 activation in colonic tissues from patients with UC.. A3AR activation inhibited inflammation by mitigating pro-inflammatory cytokine production and the NF-κB signal activation in colonic mucosa of patients with UC. A3AR activation may play a role in the pathogenesis of UC.

Topics: Adenosine; Colitis, Ulcerative; Colon; Cytokines; Down-Regulation; Humans; Inflammation; Interleukin-1beta; Intestinal Mucosa; NF-kappa B; Peptide Fragments; Purinergic P1 Receptor Agonists; Receptor, Adenosine A3; Signal Transduction; Tumor Necrosis Factor-alpha; Up-Regulation

To investigate the expression of adenosine A3 receptor (A3AR) in human colonic epithelial cells and the effects of A3AR activation on tumor necrosis factor alpha (TNF-α-) induced inflammation in order to determine its mechanism of action in human colonic epithelial cells, human colonic epithelial cells (HT-29 cells) were treated with different concentrations of 2-Cl-IB-MECA prior to TNF-α stimulation, followed by analysis of NF-κB signaling pathway activation and downstream IL-8 and IL-1β production. A3AR mRNA and protein were expressed in HT-29 cells and not altered by changes in TNF-α or 2-Cl-IB-MECA. Pretreatment with 2-Cl-IB-MECA prior to stimulation with TNF-α attenuated NF-κB p65 nuclear translocation as p65 protein decreased in the nucleus of cells and increased in the cytoplasm, inhibited the degradation of IκB-α, and reduced phosphorylated-IκB-α level significantly, compared to TNF-α-only-treated groups. Furthermore, 2-Cl-IB-MECA significantly decreased TNF-α-stimulated IL-8 and IL-1β mRNA expression and secretion, compared to the TNF-α-only treated group. These results confirm that A3AR is expressed in human colonic epithelial cells and demonstrate that its activation has an anti-inflammatory effect, through the inhibition of NF-κB signaling pathway, which leads to inhibition of downstream IL-8 and IL-1β expression. Therefore, A3AR activation may be a potential treatment for gut inflammatory diseases such as inflammatory bowel disease.

Topics: Adenosine; Colon; Epithelial Cells; HT29 Cells; Humans; Inflammation; Interleukin-1beta; Interleukin-8; NF-kappa B; Receptor, Adenosine A3; Signal Transduction; Tumor Necrosis Factor-alpha

This protocol describes microsphere-based protease assays for use in flow cytometry and high-throughput screening. This platform measures a loss of fluorescence from the surface of a microsphere due to the cleavage of an attached fluorescent protease substrate by a suitable protease enzyme. The assay format can be adapted to any site or protein-specific protease of interest and results can be measured in both real time and as endpoint fluorescence assays on a flow cytometer. Endpoint assays are easily adapted to microplate format for flow cytometry high-throughput analysis and inhibitor screening.

Topics: Animals; Biotinylation; Flow Cytometry; Fluorescence Resonance Energy Transfer; Green Fluorescent Proteins; High-Throughput Screening Assays; Humans; Inflammation; Kinetics; Microspheres; Peptide Hydrolases; Peptides; Reproducibility of Results; Temperature

The A(3) adenosine receptor (A3AR) is one of four receptor subtypes for adenosine and is expressed in a broad spectrum of tissues. In order to study the function of A3AR, a mouse line carrying a mutant A(3) allele was generated. Mice homozygous for targeted disruption of the A3AR gene, A3AR(-/-), are fertile and visually and histologically indistinguishable from wild type mice. The lack of a functional receptor in the A3AR(-/-) mice was confirmed by molecular and pharmacological analyses. The absence of A3AR protein expression in the A3AR(-/-) mice was demonstrated by lack of N(6)-(4-amino-3-[(125)I]iodobenzyl)adenosine binding to bone marrow-derived mast cell membranes that were found to express high levels of A3AR in wild type mice. In A3AR(-/-) mice, the density of A(1) and A(2A) adenosine receptor subtypes was the same as in A3AR(+/+) mice as determined by radioligand binding to brain membranes. Additionally, A(2B) receptor transcript expression was not affected by ablation of the A3AR gene. A3AR(-/-) mice have basal heart rates and arterial blood pressures indistinguishable from A3AR(+/+) mice. Functionally, in contrast to wild type mice, adenosine and the A3AR-specific agonist, 2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyl-carboxamide (2-Cl-IB-MECA), elicit no potentiation of antigen-dependent degranulation of bone marrow-derived mast cells from A3AR(-/-) mice as measured by hexosaminidase release. Also, the ability of 2Cl-IB-MECA to inhibit lipopolysaccharide-induced tumor necrosis factor-alpha production in vivo was decreased in A3AR(-/-) mice in comparison to A3AR(+/+) mice. The A(2A) adenosine receptor agonist, 2-p-(2-carboxyethyl)phenylamino)-5'-N-ethylcarboxamidoadenosine, produced inhibition of lipopolysaccharide-stimulated tumor necrosis factor-alpha production in both A3AR(-/-) and A3AR(+/+) mice. These results show that the inhibition in vivo can be mediated by multiple subtypes, specifically the A(3) and A(2A) adenosine receptors, and A3AR activation plays an important role in both pro- and anti-inflammatory responses.

Topics: Adenosine; Animals; beta-N-Acetylhexosaminidases; Blood Pressure; Gene Targeting; Heart Rate; Inflammation; Lipopolysaccharides; Mast Cells; Mice; Mice, Knockout; Protein Binding; Receptor, Adenosine A3; Receptors, Purinergic P1; RNA, Messenger; Tumor Necrosis Factor-alpha; Xanthines