Activation of adenosine receptor on gingival fibroblasts

Molecular mechanisms of inflammation in the pathogenesis of respiratory disorders in patients with pulmonary tuberculosis

Aim. To assess external respiration (ER) and its relationship with the activity of enzymes involved in purine metabolism in patients with acute and chronic forms of pulmonary tuberculosis (TB).

Materials and methods. In patients with acute and chronic TB, we assessed the activity of adenosine deaminase (ADA)-1, 2 in the blood serum (eADA), mononuclear cells, and neutrophils, the concentration of ecto-5’-nucleotidase (eNT5E) in the blood serum, the level of CD26 (dipeptidyl peptidase-4, DPPIV) in the blood serum and mononuclear cells, production of reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI) in mononuclear cells and neutrophils, as well as parameters of ER.

Results. Patients with TB were found to have an increase in the concentration of eNT5E and eADA-2 activity in the blood serum, stimulated production of ROI in neutrophils, a decrease in the concentration of DPPIV (CD26) in mononuclear cells, and a fall in the production of RNI in mononuclear cells and neutrophils. In patients with chronic TB, a decrease in the activity of ADA-1 in mononuclear cells and a fall in the concentration of DPPIV (CD26) in the blood serum were noted. In patients with acute TB, a decrease in the activity of eADA-1 in the blood serum and ADA-1 in neutrophils, reduced production of ROI in mononuclear cells, and an increase in spontaneous production of ROI in neutrophils were revealed. Correlations were found between the parameters of ER and the concentration of eNT5E in the blood serum, spontaneous production of ROI in mononuclear cells and production of RNI in neutrophils in chronic TB, as well as between eADA-2 in the blood serum, ADA-1 in neutrophils, DPPIV (CD26) activity in mononuclear cells, and ROI and RNI production in mononuclear cells and neutrophils.

Conclusion. The data obtained make it possible to associate regulation of external respiration with parameters of purine metabolism, in particular with the concentration and activity of enzymes responsible for generation and metabolism of adenosine, that determine its level outside cells and inside mononuclear cells and neutrophils, with expression of cofactor molecules, as well as with the duration of activation of cells in innate immunity, neutrophils, and monocytes/ macrophages, determined largely by the potential of adenosine regulation.

Unfolding Role of a Danger Molecule Adenosine Signaling in Modulation of Microbial Infection and Host Cell Response

Ectonucleotidases CD39 and CD73, specific nucleotide metabolizing enzymes located on the surface of the host, can convert a pro-inflammatory environment driven by a danger molecule extracellular-ATP to an adenosine-mediated anti-inflammatory milieu. Accordingly, CD39/CD73 signaling have has strongly implicated in modulating the intensity, duration, and composition of purinergic danger signals delivered to host. Recent studies have eluted potential roles for CD39 and CD73 in selective triggering of a variety of host immune cells and molecules in the presence of pathogenic microorganisms or microbial virulence molecules. Growing evidence also suggests that CD39 and CD73 present complimentary, but likely differential, actions against pathogens to shape the course and severity of microbial infection as well as the associated immune response. Similarly, adenosine receptors A2A and A2B have been proposed to be major immunomodulators of adenosine signaling during chronic inflammatory conditions induced by opportunistic pathogens, such as oral colonizer Porphyromonas gingivalis. Therefore, we here review the recent studies that demonstrate how complex network of molecules in the extracellular adenosine signaling machinery and their interactions can reshape immune responses and may also be targeted by opportunistic pathogens to establish successful colonization in human mucosal tissues and modulate the host immune response.

Lipopolysaccharide of Aggregatibacter actinomycetemcomitans up-regulates inflammatory cytokines, prostaglandin E2 synthesis and osteoclast formation in interleukin-1 receptor antagonist-deficient mice

BACKGROUND AND OBJECTIVE

The interleukin (IL)-1 receptor antagonist (Ra) binds to IL-1 receptors and inhibits IL-1 activity. However, it is unclear whether the IL-1Ra plays a protective role in periodontal disease. The purpose of this study was to compare IL-1Ra knockout (KO) and wild-type (WT) mice in regard to proinflammatory cytokine production, osteoclast formation and bone resorption in response to periodontal bacterial lipopolysaccharide (LPS).

MATERIAL AND METHODS

Peritoneal macrophages (Mφs) were obtained from 13-wk-old IL-1Ra KO and WT mice. Peritoneal Mφs were cultured with or without 10 μg/mL of Aggregatibacter actinomycetemcomitans LPS for 24 h. The levels of IL-1alpha (IL-1α), IL-1beta (IL-1β), tumor necrosis factor-α (TNF-α) and IL-6 were measured in periotoneal Mφs supernatant fluid (PM-SF) using an ELISA. Bone marrow cells were obtained from the mice and stimulated with PM-SF for 9 d, then stained with TRAP. The frequency of TRAP-positive multinucleated giant cell formation was calculated based on a fusion index. PM-SF-stimulated calvarial bone resorption was analyzed using micro-computed tomography, and calvarial histological analysis was performed using hematoxylin and eosin and TRAP staining. The expression of cyclooxygenase-2 (Cox2), prostanoid receptor EP4 (Ep4) and Rank mRNAs in bone marrow cells were measured using real-time quantitative PCR, while prostaglandin E2 (PGE2 ) production was determined by ELISA.

RESULTS

The levels of IL-1α, IL-1β, TNF-α and IL-6 in IL-1Ra KO mice PM-SF stimulated with A. actinomycetemcomitans LPS were significantly increased by approximately 4- (p < 0.05), 5- (p < 0.05), 1.3- (p < 0.05) and 6- (p < 0.05) fold, respectively, compared with the levels in WT mice. Moreover, osteoclast formation, expression of Rank, Ep4 and Cox2 mRNAs and production of PGE2 were significantly increased by approximately 2- (p < 0.05), 1.6- (p < 0.05), 2.5- (p < 0.05), 1.6- (p < 0.05) and 1.9- (p < 0.05) fold, respectively, in IL-1Ra KO mice stimulated with A. actinomycetemcomitans LPS compared with WT mice.

CONCLUSION

IL-1Ra regulates IL-1 activity and appears to reduce the levels of other inflammatory cytokines, including TNF-α and IL-6, while it also reduces expression of the EP4 receptor related to prostanoid sensitivity and osteoclast formation. These results suggest that IL-1Ra is an important molecule for inhibition of inflammatory periodontal bone resorption.

Novel effects of adenosine receptors on pericellular hyaluronan matrix: implications for human smooth muscle cell phenotype and interactions with monocytes during atherosclerosis

Hyaluronan (HA) is responsive to pro-atherosclerotic growth factors and cytokines and is thought to contribute to neointimal hyperplasia and atherosclerosis. However, the specific function of the pericellular HA matrix is likely depend on the respective stimuli. Adenosine plays an important role in the phenotypic regulation of vascular smooth muscle cells (VSMC) and is thought to inhibit inflammatory responses during atherosclerosis. The aim of this study was to examine the regulation and function of HA matrix in response to adenosine in human coronary artery SMC (HCASMC). The adenosine receptor agonist NECA (10 μM) caused a strong induction of HA synthase (HAS)1 at 6 h and a weaker induction again after 24 h. Use of selective adenosine receptor antagonists revealed that adenosine A2(B) receptors (A2(B)R) mediate the early HAS1 induction, whereas late HAS1 induction was mediated via A2(A)R and A3R. The strong response after 6 h was mediated in part via phosphoinositide-3 kinase- and mitogen-activated protein kinase pathways and was inhibited by Epac. Functionally, NECA increased cell migration, which was abolished by shRNA-mediated knock down of HAS1. In addition to HA secretion, NECA also stimulated the formation of pronounced pericellular HA matrix in HCASMC and increased the adhesion of monocytes. The adenosine-induced monocyte adhesion was sensitive to hyaluronidase. In conclusion, the current data suggest that adenosine via adenosine A2(B)R and A2(A)R/A3R induces HAS1. In turn a HA-rich matrix is formed by HCASMC which likely supports the migratory HCASMC phenotype and traps monocytes/macrophages in the interstitial matrix.

Inflammation, pain, and pressure--purinergic signaling in oral tissues

Signaling by extracellular purines such as ATP and adenosine has implications for dental research on multiple levels, with the association of purinergic signaling with inflammation, mechanical strain, and pain making the system particularly relevant for the specific challenges in the oral cavity. Oral tissues express a variety of G-protein-coupled P2Y receptors for ATP and P1 receptors for adenosine in addition to ionotropic P2X receptors for ATP. When these receptors are combined with the plethora of extracellular enzymes capable of manipulating extracellular agonist levels, a complex system for regulating oral health emerges, and recent findings have begun to identify a key role for purinergic signaling in oral pathophysiology. For example, the manipulation of extracellular ATP levels by P. gingivalis reduces inflammasome activation and apoptosis linked to P2X(7) receptor activation. Release of ATP by periodontal ligaments may link mechanical strain to bone remodeling. Activation of P2X receptors is implicated in dental pain, and receptor antagonists represent important targets for new analgesics. Altered levels of adenosine receptors in periodontal disease also suggest a role for nucleosides in dental signaling. The intricacies of the purinergic signaling system make it well-suited for the unique concerns of dental research, and future findings will doubtless confirm this importance.

Adenosine receptor stimulation by polynucleotides (PDRN) reduces inflammation in experimental periodontitis

AIM

Adenosine receptors modulate inflammation in periodontal tissues. No data are available regarding the effects of adenosine A(2A) receptor stimulation in experimental periodontitis (EPD). The aim of this study was to investigate the effects of polynucleotides (also known as polydeoxyribonucleotide, PDRN), a ligand of A(2A) receptor, in EPD in rats.

MATERIALS AND METHODS

EPD was induced ligating the cervix of the lower left first molar. Sham-EPD had no ligature. After 7 days, EPD animals were randomized to a daily treatment with vehicle gel or 0.75% PDRN gel or PDRN gel with a specific A(2A) antagonist (DMPX). Treatments lasted 7 days. Animals were then euthanized and the periodontium and surrounding gingival tissue were excised for histological evaluation and bio-molecular analysis of inflammatory (p-JNK, p-ERK, TNF-α, IL-6, HMGB-1) and apoptotic proteins (BAX and Bcl-2).

RESULTS

Vehicle-treated EPD rats showed severe inflammatory infiltrate in both gingival and periodontal ligament, as well as an enhanced expression of p-JNK, p-ERK, TNF-α, IL-6, HMGB-1 and BAX and a reduction in Bcl-2. PDRN gel restored the histological features, blunted inflammatory and apoptotic proteins expression and preserved Bcl-2 expression. DMPX abrogated PDRN positive effects.

CONCLUSION

Our data suggest that adenosine receptor stimulation by PDRN might represent a new therapeutic strategy for periodontitis.

The blockade of adenosine deaminase ameliorates chronic experimental colitis through the recruitment of adenosine A2A and A3 receptors

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-α (TNF-α), 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-α, 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-α, 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.

Reduction of N-glycolylneuraminic acid xenoantigen on human adipose tissue-derived stromal cells/mesenchymal stem cells leads to safer and more useful cell sources for various stem cell therapies

Adipose tissue is an attractive source for somatic stem cell therapy. Currently, human adipose tissue-derived stromal cells/mesenchymal stem cells (hADSCs/MSCs) are cultured with fetal bovine serum (FBS). Recently, however, not only human embryonic stem cell lines cultured on mouse feeder cells but also bone marrow-derived human MSCs cultured with FBS were reported to express N-glycolylneuraminic acid (Neu5Gc) xenoantigen. Human serum contains high titers of natural preformed antibodies against Neu5Gc. We studied the presence of Neu5Gc on hADSCs/MSCs cultured with FBS and human immune response mediated by Neu5Gc. Our data indicated that hADSCs/MSCs cultured with FBS expressed Neu5Gc and that human natural preformed antibodies could bind to hADSCs/MSCs. However, hADSCs/MSCs express complement regulatory proteins such as CD46, CD55, and CD59 and are largely resistant to complement-mediated cytotoxicity. hADSCs/MSCs cultured with FBS could be injured by antibody-dependent cell-mediated cytotoxicity mechanism. Further, human monocyte-derived macrophages could phagocytose hADSCs/MSCs cultured with FBS and this phagocytic activity was increased in the presence of human serum. Culturing hADSCs/MSCs with heat-inactivated human serum for a week could markedly reduce Neu5Gc on hADSCs/MSCs and prevent immune responses mediated by Neu5Gc, such as binding of human natural preformed antibodies, antibody-dependent cell-mediated cytotoxicity, and phagocytosis. Adipogenic and osteogenic differentiation potentials of hADSCs/MSCs cultured with heat-inactivated human serum were not less than that of those cultured with FBS. For stem cell therapies based on hADSCs/MSCs, hADSCs/MSCs that presented Neu5Gc on their cell surfaces after exposure to FBS should be cleaned up to be rescued from xenogeneic rejection.