L'adénosine est un nucléoside ubiquitaire issu de la déphosphorylation de l'ATP qui est libéré par les cellules endothéliales et les myocytes lors de l'hypoxie, de l'ischémie ou du stress oxydatif. Elle exerce un contrôle puissant sur les systèmes nerveux, immunitaire et cardiovasculaire par l'intermédiaire de quatre récepteurs membranaires : A1R, A2AR, A2BR et A3R. La compréhension de l'implication du système adénosinergique dans le système cardiovasculaire implique la possibilité technique d'un dosage de l'adénosine endogène et la quantification de l'expression de ses récepteurs. L'adénosine ayant globalement une action hypotensive (via les récepteurs A2AR) et chronotrope négative (via les récepteurs A1R), nous nous sommes intéressés à son implication chez les patients présentant des syncopes neurocardiogéniques, la bradycardie et l'hypotension étant 2 signes cardinaux dans ce syndrome. Les manifestations cliniques de cette affection peuvent être reproduites par le test d'inclinaison (HUT) et/ou le test à l'ATP. Dans un premier temps nous avons réalisé des dosages d'adénosine plasmatiques chez ces patients au moment d'un test d'inclinaison. Les concentrations en adénosine étaient élevées chez les patients présentant un test positif. Par la suite, nous avons comparé les concentrations en adénosine plasmatiques et l'expression des récepteurs A2A en fonction du résultat du test d'inclinaison et du test à l'ATP. / Adenosine is a ubiquitous nucleoside that comes from the dephosphorylation of ATP and which is released during hypoxia or oxidative stress, by endothelial cells and myocytes. Adenosine interacts on its cell surface receptors, namely A1R, A2AR, A2BR and A3R, to exert physiological effects on target tissues. Our knowledge about the adenosinergic system was improved because of our ability to measure adenosine plasma levels and to quantify its receptors expression. Because adenosine, via A1 or A2A receptor activation leads to bradycardia and hypotension, we first tried to understand the implication of the adenosinergic system in patients with neurocardiogenic syncope (NMS for neutrally mediated syncope). Indeed, this syndrome is characterized by relative or absolute bradycardia associated with a drop in blood pressure and a loss of consciousness. The symptomatology can be reproduced by the tilt test (HUT) or by the intravenous administration of ATP (ATP test). First, we measured adenosine plasma levels in patients with NMS just before and during HUT. We found that adenosine plasma levels were higher in patients with a positive HUT. Then, we compared adenosine plasma levels and the expression of A2A receptors in patients with NMS depending on the result of HUT and ATP-test. We found that elevated adenosine plasma levels and A2A receptors overexpression were associated with positive HUT. On the opposite, low adenosine plasma levels and normal expression of A2A receptor were associated with positive ATP test.

Mast cells are pivotal effector cells in the pathogenesis of allergic and inflammatory diseases. Activation of FcepsilonRI in mast cells by antigen initiates a complex series of biochemical events leading to the release and synthesis of myriads of chemical mediators and cytokines. Adenosine is an endogenous nucleoside formed from cleavage of AMP by the enzyme 5'-nucleotidase. It exerts modulating effects in a large number of cellular systems by acting through four distinct subtypes of adenosine receptors (A1, A 2A, A2B and A3) which belong to the G-protein-coupled receptor (GPCR) family. Increasing evidence have been provided to show that adenosine plays a role in the pathophysiology of asthma through a mast cell dependent mechanism. / Pharmacological studies using specific adenosine agonists and antagonists revealed that A1 receptor was responsible for the potentiating effect of adenosine with the involvement of the pertussis toxin-sensitive Galphai-protein. Conversely, inhibition of HCMC activation was mediated by A2B receptor and was accompanied by the elevation of cAMP level suggesting the participation of Galphas-protein. / Taken together, the current studies explored the dual effect of adenosine on human mast cells activation which enhanced our understanding of adenosine receptor biology. The effectiveness of adenosine in modulating the important mast cell activation pathways definitely facilitates the rational exploitation of these receptors as therapeutic targets that could be converted into clinical benefits for asthmatic patients. / To better characterize the effect of adenosine on human mast cell under asthmatic environment, we incubated HCMC under different inflammatory condition found in asthmatic, including toll-like receptor (TLR) ligands and inflammatory cytokines. Functional studies on mediator release from HCMC indicated that out of all tested substances, Peptidoglycan (PGN) pre-incubation enhanced the IL-8 synthesis from HCMC in response to low concentration of adenosine (10-9--10-7 M). / We also investigated the action of adenosine on key signal transduction pathways involved in mast cells activation. Study on intracellular calcium concentration ([Ca2+]i) revealed that low concentration of adenosine (10-8 M) through activation of PI3Kgamma significantly enhanced Ca2+ influx. In contrast, high concentration of adenosine at 10-4 M substantially inhibited [Ca2+] i in response to anti-IgE. Furthermore, investigation on intracellular signaling molecules provided evidence that adenosine at concentrations over 10-6 M does-dependently inhibited the immunoglobulin (IgE)-dependent activation of ERK, JNK or NF-kappaB pathways, whereas enhancement of IkappaBalpha was found on low concentration of adenosine. The above observation help to justify the dual action of adenosine on anti-IgE-induced mediators release from HCMC. Our investigation further suggested that adenosine may inhibit HCMC activation through a novel cAMP-dependent, but PKA- and EPAC-independent, signaling pathway. / We generated human cultured mast cells (HCMC) from human buffy coat and confirmed the expression of all adenosine receptor subtypes in them. We showed that adenosine alone did not induce HCMC degranulation and cytokine release. However, adenosine and the non-selective agonist, 5'-N-Ethylcarbox-amidoadenosine (NECA), produced a biphasic response on anti-IgE induced mast cell activation. An enhancement of HCMC activation was observed with low concentrations of adenosine and NECA (10-9--10-7 M), whereas a predominant inhibitory action was observed at concentrations higher than 10-6 M. / Yip, Kwok Ho. / Adviser: Alaster H.Y. Lau. / Source: Dissertation Abstracts International, Volume: 73-03, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 237-263). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Qi Wei. / "November 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 158-185). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

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Improved sequencing technologies have created an explosion of sequence information that is analyzed and proteins are annotated automatically. Annotations are made based on similarity scores to previously annotated sequences, so one misannotation is propagated throughout databases and the number of misannotated proteins grows with the number of sequenced genomes. A systematic approach to correctly identify the function of proteins in the amidohydrolase superfamily is described in this work using Clusters of Orthologous Groups of proteins as defined by NCBI. The focus of this work is COG1816, which contains proteins annotated, often incorrectly, as adenosine deaminase enzymes. Sequence similarity networks were used to evaluate the relationship between proteins. Proteins previously annotated as adenosine deaminases: Pa0148 (Pseudomonas aeruginosa PAO1), AAur_1117 (Arthrobacter aurescens TC1), Sgx9403e and Sgx9403g, were purified and their substrate profiles revealed that adenine and not adenosine was a substrate for these enzymes. All of these proteins will deaminate adenine with values of kcat/Km that exceed 105 M-1s-1. A small group of enzymes similar to Pa0148 was discovered to catalyze the hydrolysis of N-6-substituted adenine derivatives, several of which are cytokinins, a common type of plant hormone. Patl2390, from Pseudoalteromonas atlantica T6c, was shown to hydrolytically deaminate N-6-isopentenyladenine to hypoxanthine and isopentenylamine with a kcat/Km of 1.2 x 107 M^-1 s^-1. This enzyme does not catalyze the deamination of adenine or adenosine. Two small groups of proteins from COG1816 were found to have 6-aminodeoxyfutalosine as their true substrate. This function is shared with 2 small groups of proteins closely related to guanine and cytosine deaminase from COG0402. The deamination of 6-aminofutalosine is part of the alternative menaquinone biosynthetic pathway that involves the formation of futalosine. 6-Aminofutalosine is deaminated with a catalytic effeciency of 105 M-1s-1 or greater, Km’s of 0.9 to 6.0 µM and kcat’s of 1.2 to 8.6 s-1. Another group of proteins was shown to deaminate cyclic- 3’, 5’ -adenosine monophosphate (cAMP) to produce cyclic-3’, 5’-inosine monophosphate, but will not deaminate adenosine, adenine or adenosine monophosphate. This protein was cloned from a human pathogen, Leptospira interrogans. Deamination may function in regulating the signaling activities of cAMP.

Adenosine and adenosine analogues are recognised as cardioprotective agents due to the responses that they induce through the activation of myocardial adenosine receptors. Antioxidants such as nitroxide radicals have also been found to possess cardioprotective properties in biological systems, namely through their ability to scavenge the oxygen-based free radicals that are potentially damaging to tissues and cells. It was envisaged that the linking of an antioxidant moiety to adenosine would produce an adenosine analogue that activates adenosine receptors and also scavenges oxygen-derived free radicals in the body. Consequently, one aim of this project was to synthesise a series of adenosine analogues that possessed a nitroxide or a phenolic antioxidant at the N6 position of the adenosine skeleton. Allosteric ligands have several advantages over orthosteric ligands as potential therapeutic agents, and research into the allosteric enhancement of adenosine receptors is a burgeoning field. It was envisaged that the linking of an antioxidant moiety to an allosteric enhancer would produce a compound that enhances the response of endogenous activation of adenosine receptors and also scavenges oxygen-based free radicals in the body. Consequently, a second aim of this project was to synthesise a series of allosteric enhancers of the A1 adenosine receptor that possessed antioxidant capability endowed by a nitroxide or a phenolic antioxidant functionality. This project has resulted in the synthesis and characterisation of 19 novel N6 substituted adenosine analogues, and additionally 12 novel derivatised thiophenes. Each of the target compounds was tested for its ability to bind to each of the adenosine receptor subtypes and some analogues were found to be potent and selective adenosine receptor agonists.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Missouri--Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves: 145-165). Also available on the Internet.

Thesis (Ph. D.)--University of Virginia, 2008. / Title from title page. [gamma] and [epsilon] in title are the Greek letters. Includes bibliographical references. Also available online through Digital Dissertations.